Prevalence of bipolar II disorder in outpatient depression: a 203-case study in private practice.

Of 203 consecutive major depressed outpatients in a private setting, 45% had bipolar II disorder, 51% had unipolar depression, and 4% had bipolar I disorder. The observed prevalence of bipolar II disorder was higher then previously reported in clinical samples (10-40%). Bipolar II disorder had age at baseline and onset lower than unipolar depression, and more atypical features. Other variables (baseline depression severity, number of depressive episodes, psychosis, chronicity, comorbidity) were similar, suggesting that the depressive phase of bipolar II disorder differs only in one, but important, dimension (atypical features) from unipolar depression in a private setting.