It has been suggested that early- and late-onset forms of obsessive-compulsive disorder (OCD) may stem from different neurobiological substrates manifesting themselves through particular phenotypic profiles. Our study aimed to assess the existence of clinical and therapeutic differences between adult patients with early- and late-onset OCD (EOCD and LOCD, respectively). Sixty-six patients with OCD were consecutively recruited among individuals seeking treatment in a university hospital clinic for anxiety and depressive disorders. Patients with EOCD (n=33) and LOCD (n=33) were compared and contrasted with regard to clinical and therapeutic characteristics using the two tailed t test for continuous variables and the Pearson's goodness of fit Chi-square test for categorical ones; Fisher's exact test was employed when indicated. We found that, compared to their LOCD counterparts, adult patients with EOCD were characterized by (1) male gender predominance, (2) greater number of clinically significant obsessions and compulsions, (3) higher frequency of rituals repetition, (4) increased severity of obsessive-compulsive symptoms at baseline, and (5) greater number of required therapeutic trials during the follow-up. However, no significant differences between groups were noted in the final treatment outcome. Our results are consistent with previous studies suggesting that EOCD may represent a more severe subtype of this disorder.