Controversy exists about the relationship between postpartum and nonpostpartum depression in both research and practice. While some researchers argue that these diagnoses cannot be differentiated, others insist that postpartum depression is distinct. The construct validity of the diagnosis "postpartum depression" is evaluated by critically reviewing the empirical evidence regarding prevalence, symptomatology, course, duration, relapse, and etiology. The literature suggests that women are at elevated risk for depression in the postpartum period. However, postpartum depressive episodes tend to be mild and to resolve quickly, which suggests that postpartum depression is best conceptualized as an adjustment disorder. Etiologically, postpartum depression is related to the same variables that predict nonpostpartum depression. These findings suggest that postpartum depression does not differ qualitatively from nonpostpartum depression. The implications of this conclusion for research and treatment are considered.