The differential effects of serotonin-reuptake inhibitors on obsessive–compulsive disorder (OCD) were sufficient to presume that a serotonin regulatory disorder is the most essential part of the pathophysiology of OCD. In patients with OCD, however, a high-dose of serotonin-reuptake inhibitor monotherapy may not be sufficient, and approximately half of patients were noted to be treatment-resistant. As results from previous studies have shown, there have been positive treatment responses to the dopaminergic antagonists. This suggests that other neurotransmitter systems, such as dopamine, are involved in the pathophysiology of OCD. Preclinical, neuroimaging and neurochemical studies have provided evidence demonstrating that the dopaminergic system is involved in inducing or aggravating the symptoms that are indicative of OCD. In this article, we review the dopaminergic system in OCD pathophysiology as well as reviewing the effect of drugs that act on dopaminergic activity in OCD.