[Page 511]Investigations of gender and sex differences in the prevalence and clinical characteristics of bipolar disorders can increase our knowledge about the disorders and improve assessment and effective management. Clinical and epidemiological studies indicate that rates of bipolar I disorder are comparable across the genders, although there appears to be higher rates of bipolar II disorder in women. In addition to prevalence rates, the study of gender differences in the phenomenology and course of illness in bipolar disorder has only recently become a focus of research. This overview identifies some gender-based differences that might reflect varying biological and psychological causal factors that affect the risk of bipolar disorder, its longitudinal course, and response to treatment—while also highlighting the minimal degree of research that has been ...