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.