Objective: To investigate the clinical implications of obsessive-compulsive disorder (OCD) and ADHD comorbidity in adults. Method: The OCD patients who had and had no diagnosis of adulthood ADHD were compared in terms of several demographic and clinical variables. Results: The mean number of obsessions and compulsions; hoarding, symmetry, and miscellaneous obsessions; ordering/arranging and hoarding compulsions; total, attentional, and motor subscale scores of Barratt Impulsivity Scale (BIS)-11 were more frequent among the patients with OCD-ADHD. The mean age of onset was more likely to be earlier in ADHD-OCD group than in OCD group. Impulsivity, symmetry obsessions, and hoarding compulsions strongly predicted the coexistence between ADHD and OCD. Conclusion: OCD-ADHD comorbidity in adults seemed to be associated with an earlier onset of OCD, with the predominance of impulsivity, and with a different obsessive-compulsive symptom (OC) profile from OCD patients without a diagnosis of ADHD.