Bipolar disorder is characterized by recurrent episodes of mania (bipolar 1) or hypomania (bipolar 2) and depression. Using DSM-IV criteria, prevalence rates are 1%–2%. Epidemiological studies using broader criteria have proposed a bipolar spectrum ‘with a prevalence rate of 3%–7%’. Peak age of onset is late adolescence. A gap between onset episode and diagnosis and treatment is common. Hypomania often goes unrecognized or unreported, leading to a misdiagnosis of depression. Substance abuse comorbidity is high and may confound diagnosis. Suicide risk is 20 times the general population rates with a 5:1 ratio of attempts to completed suicides compared with 18:1 in the general population. The past decade has seen significant advances in treatment of bipolar disorder providing a strong evidence base for efficacy. However, 40%–50% of patients report subthreshold symptoms, predominantly depression between illness episodes contributing to the high lifetime rate of functional impairment.