Objective: Our aim is to investigate the impact of childhood ADHD comorbidity on the clinical features of obsessive compulsive disorder (OCD). Method: Ninety-five adult outpatients with a diagnosis of OCD were assessed by using the Schedule for Affective Disorders and Schizophrenia for School Age Children-Present and Lifetime Version, ADHD module, and the Yale-Brown Obsessive Compulsive Scale. Patients with or without childhood ADHD were compared in terms of the sociodemographic and clinical features, psychiatric comorbidities, and rating scales. Results: The rate of episodic course of OCD (p < .001), religious and sexual obsessions (p = .009, p = .020, respectively), lifetime comorbidity of bipolar disorder (BD), social anxiety disorder (SAD; p = .001, p = .009, respectively), and tic disorder (TD) comorbidity (p < .001) were higher in the OCD + ADHD group than in the OCD without ADHD group. Conclusion: Childhood ADHD may be associated with higher rates of BD, SAD, and TD comorbidity and episodic course of OCD as well as higher frequency of certain types of obsessions.