Researchers consider obsessive-compulsive disorder (OCD) to be an anxiety disorder, but it often shows comorbidity with other disorders in the affective spectrum. Epidemiological and clinical studies have shown a strong association between OCD and mood disorders. In addition, some reports show the patients with OCD have attentional-processing impairments regarding emotional information. However, research has not revealed the exact nature and degree to which OCD constitutes an affective problem. In this review, we discuss the affective aspects of OCD and the relationship between OCD and mood disorders.