This study was designed to assess the prevalence of Attention-Deficit/Hyperactivity Disorder (ADHD) and Oppositional Defiant Disorder (ODD) in a representative sample of second grade students from a country in a region where no previous rates are available (Turkey). The second aim is to evaluate the differences in ADHD and ODD prevalence rates among four different waves with one-year gap in reassessments. Sixteen schools were randomly selected and stratified according to socioeconomic classes. The DSM-IV Disruptive Behavior Disorders Rating Scale (T-DSM-IV-S) was delivered to parents and teachers for screening in around 1500 children. Screen positive cases and matched controls were extensively assessed using the K-SADS-PL and a scale to assess impairment criterion. The sample was reassessed in the second, third and fourth waves with the same methodology. The prevalence rates of ADHD in the four waves were respectively 13.38%, 12.53%, 12.22% and 12.91%. The ODD prevalence was found to be 3.77% in the first wave, 0.96% in the second, 5.41% in the third and 5.35% in the fourth wave. Mean ODD prevalence was found to be 3.87%. The prevalence rates of ADHD in the four waves were remarkably higher than the worldwide pooled childhood prevalence. ADHD diagnosis was quite stable in reassessments after one, two and three years. A mean ODD prevalence consistent with the worldwide-pooled prevalence was found; but diagnostic stability was much lower compared to ADHD.

Objective: The objective was to examine the frequency of comorbid disorders in children and adolescents with ADHD in Turkey and to evaluate the distribution of comorbidities according to the subtypes of ADHD and sociodemographic features. Method: The sample consisted of 1,000 children, 6 to 18 years of age, including 242 females and 758 males, from Ege University who were diagnosed with ADHD. Results: The overall prevalence rate of psychiatric comorbidity in the study was 56.3%. The most frequently observed comorbidity was oppositional defiant disorder with a rate of 37.4%. Conduct disorder, depressive disorder, obsessive-compulsive disorder, and anxiety disorder accompanied ADHD, respectively. The results revealed that 70.2% of the children with ADHD-Combine type had at least one psychiatric comorbidity. Oppositional defiant disorder, conduct disorder, depressive disorder, and obsessive-compulsive disorder accompanied ADHD-Combine type in 54.6%, 12.6%, 8.1%, and 8.8% of the participants, respectively. Conclusion: These findings provide valuable information about the comorbid disorders in children and adolescents with a very large clinical sample of ADHD children.