Clinical research has documented a bidirectional overlap between Tourette's disorder (TD) and obsessive-compulsive disorder (OCD) from familial-genetic, phenomenological, comorbidity, and natural history perspectives. Patients with Tourette's disorder plus obsessive-compulsive disorder (TD+OCD), a putative subtype, share features of both. The purpose of this exploratory study was to evaluate correlates of patients with TD, OCD, and TD+OCD to determine whether TD+OCD is a subtype of TD, OCD, or an additive form of both. Sixty-one subjects with TD, OCD, or TD+OCD were evaluated with the Structured Clinical Interview for DSM-III-R supplemented with additional modules. The three groups differed in the rates of bipolar disorder (p <.04), social phobia(p <.02), body dysmorphic disorder (p <.002), attention deficit hyperactivity disorder (p <.03), and substance use disorders (p <.04). These findings were accounted for by the elevated rates of the disorders in the TD+OCD group compared with the TD and OCD groups. These finding are most consistent with the hypothesis that TD+OCD is a more severe disorder than TD and OCD and may be more etiologically linked to TD than to OCD. These findings highlight the importance of assessment of the full spectrum of psychiatric comorbidity in patients with TD and OCD.