Obsessive-compulsive disorder (OCD) is a frequent and chronic psychiatric disorder that has been linked closely to the serotonin system mainly because of the antiobsessional efficacy of selective serotonin reuptake inhibitors (SSRIs). A limitation of the serotonin hypothesis of OCD is that a substantial number of the patients with OCD show no significant improvement after an adequate trial with SSRIs. There is substantial evidence that these patients may benefit from addition of antipsychotics to their ongoing SSRI treatment, suggesting that dopamine also might play a role in the pathophysiology of OCD. In this review, the preclinical and clinical evidence on the role of dopamine in OCD is summarized.