Premenstrual dysphoric disorder (PMDD) is a premenstrual mood disorder that cyclically recurs during the majority of menstrual cycles. It is included under the category of “depressive disorders not otherwise specified” in DSM-IV. Given the placement of PMDD with other mood disorders in DSM-IV, the evidence suggesting an association between PMDD and other mood disorders is examined. Primary reports on the epidemiology, phenomenology, family history, psychobiology, and treatment of PMDD were examined for features that are commonly found in other mood disorders. There is an overlap in the symptoms experienced by women with PMDD and patients with other mood disorders. As in patients with other mood disorders, past episodes of mood disorder and family history of mood disorder are common in women with PMDD. Selected biological markers differentiate women with PMDD from controls, and some but not all antidepressants are effective in the treatment of PMDD. Many features of PMDD support its inclusion in the DSM-IV category of mood disorders. However, a number of factors (biological and cognitive studies, treatment response) differentiate PMDD from other mood disorders.