Differential diagnosis of attention deficit hyperactivity disorder (ADHD) is one of the most important and complex issues in child and adolescent clinical psychology, because both groups of disorders can be associated with inattention, restlessness, difficulty in completing homework, impaired academic performance, and problems with social interactions. The apparent similarity of some symptoms may lead to incorrect diagnosis, ignoring the co-occurrence disorder, or choosing inappropriate therapeutic intervention. Therefore, a precise distinction between these disorders requires an examination of the developmental history, time pattern of symptoms, situations of occurrence of behavior, emotional experiences of the child, cognitive function, and family and educational conditions. Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by a persistent pattern of inattention or impulsivity and can impair a child's academic, social, and family functioning. In contrast, anxiety disorders are a group of mental health problems that are characterized by fear, worry, or excessive anxiety and difficulty in managing these experiences, and may manifest themselves in certain situations or in different areas of life. The fundamental difference between the two groups is in the nature and underlying mechanisms of symptoms, so that attention problems in ADHD are usually associated with a persistent pattern of difficulty in maintaining attention, organizing, tracking activities, and controlling impulses, while inattention in anxiety disorders may be more likely to be caused by mental preoccupation with worry, threat monitoring, fear of failure, or expectation of negative consequences. For example, a child with ADHD may pay attention to unrelated environmental stimuli while doing an assignment, lose their belongings, or forget activity steps, even when there is no obvious sign of worry. In contrast, an anxious child may not be able to maintain focus due to concerns about making mistakes, teacher reactions, or peer evaluations, and may devote much of their cognitive capacity to worrying thoughts. Of course, this distinction is not absolute, and both mechanisms may be present in the same child, so observing neglect alone is not enough to determine a diagnosis. One of the most important axes of differential diagnosis is the examination of developmental history and the time of onset of symptoms. ADHD usually has its roots in development, and its symptoms must have started in childhood based on diagnostic criteria; in the DSM-5-TR framework, the presence of several symptoms before the age of twelve is one of its diagnostic criteria. In the evaluation, the specialist examines whether there have been difficulties with attention, organizing, or controlling impulses from the early years of development, or whether the problems appeared mainly after a stressful event, increased academic pressure, or the formation of intense worries. The relatively sudden onset of concentration problems at the same time as increased anxiety can raise the possibility of a role for emotional factors, but it does not rule out ADHD alone. Likewise, the presence of symptoms from the early years of life does not preclude the diagnosis of co-occurring anxiety. In ADHD, to be diagnosed, symptoms must be observed in more than one setting, such as home and school, and have a significant interfering with the child's functioning or development. Anxiety disorders may also occur in several settings, but their severity can depend on specific stimuli; for example, a child may perform relatively well at home, but may experience severe distress when separated from parents, being in public, or facing an academic assessment. Examining differences in a child's performance in different situations can help to better understand the factors influencing behavior, although no environmental pattern alone makes the diagnosis conclusive. In the area of ADHD and restlessness, it is particularly important to distinguish between ADHD-induced motor activity and anxiety-related restlessness. A child with ADHD may frequently get up, fail to take turns, answer questions before the end of the question, or show difficulty in situations that require expectation and control of behavior. These behaviors are usually part of a broader and enduring pattern of inattention or impulsive hyperactivity. In contrast, the restlessness of an anxious child may be more associated with muscle tension, worry, fear of consequences, frequent questions about safety, or attempts to reduce the sense of danger. For example, a child who constantly moves his pencil before a test, gets up from a chair, or asks questions about a test result may be restless in response to functional anxiety; however, if the same child has a persistent pattern of impulsivity and difficulty controlling activity in other situations, it is also necessary to investigate ADHD. In differential diagnosis, the quality of attention and the type of cognitive errors are also important. In ADHD, the child may execute instructions due to distraction, forgetfulness, difficulty following steps, or poor organization. In anxiety disorders, the child may know the instructions, but may not be able to use his or her ability well due to constant worry, fear of making mistakes, or being mentally preoccupied with evaluating others. Sometimes an anxious child completes assignments too slowly, checks their answers repeatedly, or needs adult approval to ensure that the task is correct. In contrast, a child with ADHD may complete assignments in a hurry, ignore details, or deliver work without reviewing the answers. However, these patterns are merely possible symptoms and should not be used as definitive diagnostic rules because anxiety can cause avoidance and procrastination, and ADHD may also be associated with compensatory perfectionism or worry about previous failures. Examining the child's subjective experience helps distinguish between the two situations. In anxiety disorders, the child may report frequent concerns about their own or family's health, safety, separation, breakup, social exclusion, or future events. Sometimes these worries appear in the form of physical symptoms such as stomach pain, headache, nausea, palpitations, sweating, or sleep disturbances. In ADHD, functional problems may be more associated with forgetfulness, difficulty managing time, losing belongings, impulsivity, and an inability to complete activities, with pervasive worry being the main cause of these problems. However, young children may not be able to express their concern verbally, and their anxiety may manifest through crying, irritability, clinging to parents, refusing to go to school, or avoiding activities. Therefore, the absence of verbal reporting of concern does not rule out anxiety, and assessment should use age-appropriate methods. Examining educational and social history also provides valuable information. In ADHD, there may be a history of losing belongings, forgetting homework, difficulty following instructions, interrupting others' speech, or persistent problems keeping appointments. In social anxiety, the child may avoid public speaking, responding in class, participating in group activities, or interacting with unfamiliar people because they are afraid of being humiliated, making mistakes, or being judged negatively. In separation anxiety, a child's difficulties may intensify when separated from a caregiver, going to school, or sleeping away from their parents. In generalized anxiety, worry may encompass several areas of life and be associated with stress, irritability, fatigue, or sleep problems. It is important to diagnose the type of anxiety because the apparent origin of similar behavior can vary; for example, school refusal may be caused by separation anxiety, social anxiety, learning difficulties, bullying, depression, or difficulties associated with ADHD. Careful consideration of underlying factors prevents hasty attribution of behavior to a disorder. The role of the family in the differential diagnosis process is crucial, as parents can provide information about the onset of symptoms, sleep patterns, behavior at home, the child's response to changes, and recurring concerns. At the same time, parents' perceptions may be influenced by family stress levels, behavioral expectations, and personal experiences, so their report should be reviewed alongside information from the child and teachers. Teachers can usually provide important information about maintaining attention in class, following instructions, completing assignments, taking turns, interacting with peers, and performance differences in different lessons. For example, if a child is attentive to a favorite activity but is inattentive to difficult or lengthy tasks, motivation, task difficulty level, functional anxiety, and ADHD characteristics should all be considered. The ability to concentrate in engaging activities alone does not rule out ADHD, as the severity of symptoms can vary with the structure of the activity and the amount of reward. Similarly, poor performance in the classroom alone is not indicative of attention impairment and may be associated with anxiety, learning difficulties, sleep deprivation, or poor educational conditions. From a clinical assessment perspective, differential diagnosis should be based on comprehensive clinical interviewing, developmental history, multi-source information, and review of formal diagnostic criteria. Standard ADHD and anxiety assessment questionnaires can help identify symptomatic patterns and identify areas for further investigation, but no single scale is a substitute for specialized assessment. Tools such as ADHD grading scales, child anxiety questionnaires, and structured or semi-structured diagnostic interviews may be selected based on the child's age, language, and condition. In addition to the main symptoms, the assessment should examine the severity of the dysfunction, duration of symptoms, context of occurrence, and possible explanatory factors. Also, it is necessary to investigate other problems such as learning disorders, sleep disorders, vision or hearing problems, depression, trauma-related disorders, and other neurodevelopmental conditions if there are related symptoms. Irritability, restlessness, or poor concentration should not be attributed to ADHD or anxiety without adequate assessment. One of the major challenges of differential diagnosis is the simultaneity of ADHD and anxiety disorders. Some children face persistent difficulties with attention and impulse control, as well as clinical anxiety or fear at the same time. Frequent experience of academic failure, conflict with peers, or receiving negative feedback may contribute to the formation of secondary anxiety in some children with ADHD; on the other hand, anxiety can exacerbate problems with concentration and organization. In this situation, trying to choose only one diagnosis may overlook an important part of the child's problems. The specialist should examine whether the symptoms of both disorders independently meet the diagnostic criteria and what contribution each contributes to the dysfunction. This distinction is also important in treatment planning, as effective treatment for a disorder may not solve all the problems caused by the co-occurrence disorder. In practical terms, accurate diagnosis can help choose interventions that are appropriate to the child' s needs. For children with ADHD, behavioral interventions, parental education, educational support, and planning to improve the organization and management of tasks are important options, and in some cases, pharmacological treatment is discussed with evaluation and follow-up by a specialist. In anxiety disorders, cognitive-behavioral therapy, gradual exposure tailored to the type of anxiety, coping skills training, and targeted family involvement are evidence-based approaches. When both disorders are present, the treatment plan should be designed to address attention problems, behavior control, and emotional concerns in a coordinated manner. School support can include clear instructions, breaking down long assignments into smaller stages, reducing distractions, providing appropriate rest opportunities, and avoiding humiliation or punishment for the symptoms of the disorder. In anxious children, it is important to provide emotional support and the opportunity to gradually cope with difficult situations, but support should not lead to a permanent avoidance of essential activities. Limitations of differential diagnosis include overlap of symptoms, children's difficulty in expressing internal experiences, differences in reporters, and environment-dependent behavioral changes. Also, a child's symptoms may change during development, and their severity may be influenced by environmental pressures, sleep quality, family relationships, and educational circumstances. Therefore, in complex cases, multi-stage assessment and longitudinal follow-up may be necessary to clarify the pattern of symptoms. The outcome of the assessment should be based on sufficient evidence and labeling based on a single behavior or a questionnaire should be avoided. Overall, the differential diagnosis of ADHD from anxiety disorders in children requires simultaneous attention to developmental history, the nature of inattention and restlessness, the presence of worry and fear, avoidance patterns, functioning in different environments, and the possibility of concurrent disorders. Distinguishing between attention problems caused by neurodevelopmental pattern and concentration problems related to anxious mental occupation, along with a comprehensive study of individual and environmental factors, can increase the accuracy of diagnosis and the appropriateness of the intervention. A multidimensional, evidence-based approach that is appropriate to the child's developmental characteristics, in addition to reducing the probability of misdiagnosis, provides the ground for improving academic performance, emotion regulation, social relationships, and quality of life of the child and family.