The lifetime rates of obsessive-compulsive disorder (OCD) among subjects with histories of (1) bipolar disorder, (2) major depressive disorder but not of hypomania or mania (unipolar disorder), and (3) any Axis I disorder defined in DSM-III other than bipolar or unipolar disorders (i.e., 'other' disorder) was determined using the Epidemiologic Catchment Area (ECA) data base. The strengths of the relationships between OCD and diagnostic group, as well as between OCD and suicidality, were assessed in a multivariate logistic regression analysis. The lifetime rates of OCD among subjects with bipolar, unipolar and other Axis I disorder are 21.0, 12.2, and 5.9%, respectively. The odds ratios of subjects with bipolar and unipolar disorders meeting the criteria for OCD relative to subjects with any other Axis I disorder are 3.2 and 1.6, respectively. The odds ratio of subjects with bipolar disorder meeting the criteria for OCD relative to subjects with unipolar disorder is 2.0. The rates of panic disorder among subjects with bipolar disorder who do and do not meet the criteria for OCD are 37.1 and 16.7%, respectively. The ECA data base supports the conclusion that the lifetime rate of comorbidity for OCD is particularly high among bipolar subjects. OCD may be associated with panic disorder. These data highlight the potential value of clinical study of comorbidity for OCD in bipolar illness.