INTRODUCTION Our aim is to investigate the prevalence of comorbidity of anxiety disorders (AD) among patients newly diagnosed with attention deficit hyperactivity disorder (ADHD) and to compare symptom severity of ADHD and sociodemographic parameters between patients with and without AD. METHODS Among 1683 children and adolescents admitted to Kocaeli University Medical Faculty, Child and Adolescent Mental Health Outpatient Clinic, 447 children and adolescents, who were preliminarily diagnosed as ADHD by clinical interview based on Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV), were invited to participate in the second phase of the study. Kiddie Schedule for Affective Disorder and Schizophrenia, Present and Lifetime-Turkish Version were applied to children and adolescents with ADHD and one of their parents to support the diagnoses of both ADHD and AD. Mothers, fathers, and teachers of the children were asked to complete DSM-IV-Based Child and Adolescent Behavior Disorders Screening and Rating Scale. RESULTS Our study group comprised 170 children and adolescents diagnosed with ADHD of whom 19.4% were girls and 80.6% were boys; 27.6% of patients diagnosed with ADHD showed AD comorbidity. Age of the parents at birth of the patients with AD was significantly lower than that of patients without AD. CONCLUSION In line with the previous studies, the comorbidity rate of AD was found to be higher among patients with ADHD than general population and clinical sample without ADHD. The possibility of comorbidity of AD in patients with ADHD should be considered because higher rates of AD are observed in ADHD and comorbidities of AD.