ABSTRACT
The longitudinal association of depression with hypomania was proposed as a distinct bipolar subtype over three decades ago (Dunner et al., 1976a), and was subsequently formally defined as a diagnostic entity called bipolar II disorder in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) in 1994 (American Psychiatric Association [APA], 1994). However, controversies regarding its diagnostic criteria, validity, boundaries with other disorders, and treatment still exist. The meaningful application of a diagnosis of bipolar II disorder requires an understanding of its core features, heterogeneous aetiology, diagnostic boundaries and treatment options.
