BACKGROUND Anxiety morbidity in general is frequent and harmful in bipolar disorder. Little is known, however, whether obsessive-compulsive comorbidity entails particular effects. This report aims to evaluate the prevalence and impact of obsessive-compulsive disorder (OCD) comorbidity in a relatively large clinical sample of bipolar disorder, with other lifetime anxiety comorbidities used as a more rigorous control group. METHODS A cross-sectional study in a consecutive clinical sample, with anxiety comorbidity derived from the intake Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, was conducted. Anxiety was assessed with the Hamilton Anxiety Rating Scale. The Young Mania Rating Scale and the Hamilton Depression Rating Scale were used to assess (hypo)manic and depressive symptoms. The domains of the WHOQOL BREF were used to evaluate quality of life. RESULTS Lifetime prevalence of OCD comorbidity was 12.4%. No cases of OCD were detected during mania. Compared with subjects with no anxiety comorbidity, those with lifetime OCD were more likely to have a history of suicide attempts, rapid cycling, and alcohol dependence. Patients with OCD had a lower score on all domains of the WHOQOL. Compared with those with other lifetime anxiety disorders, those with OCD had more anxiety, which mediated a lower WHOQOL social domain. CONCLUSIONS Bipolar disorder patients with obsessive-compulsive comorbidity have a number of indicators of an overall more severe illness. The presence of more anxiety symptoms and a lower social quality of life may be more specific features of the bipolar-OCD comorbidity.