Research on postpartum mood disorders has focused primarily on major depressive disorder, bipolar I disorder, and puerperal psychosis and has largely ignored or neglected bipolar II disorder. Hypomanic symptoms are common after delivery but frequently unrecognized. DSM-IV does not consider early postpartum hypomania as a significant diagnostic feature. Although postpartum hypomania may not cause marked impairment in social or occupational functioning, it is often associated with subsequent, often disabling depression. Preliminary evidence suggests that bipolar II depression arising in the postpartum period is often misdiagnosed as unipolar major depressive disorder. The consequences of the misdiagnosis can be particularly serious because of delayed initiation of appropriate treatment and the inappropriate prescription of antidepressants. Moreover, no pharmacological or psychotherapeutic studies of bipolar postpartum depression are available to guide clinical decision making. Also lacking are screening instruments designed specifically for use before or after delivery in women with suspected bipolar depression. It is recommended that the treatment of postpartum bipolar depression follow the same guidelines as the treatment of nonpuerperal bipolar II depression, using medications that are compatible with lactation.