The literature on the lifetime prevalence of the bipolar spectrum suggests rates of 3-6.5%. The Zurich cohort study identified a prevalence rate up to age 35 of 5.5% of DSM-IV hypomania/mania and a further 2.8% for brief hypomania (recurrent and lasting 1-3 days). The validity of DSM-IV hypomania and brief hypomania was demonstrated by a family history of mood disorders, a history of suicide attempts and treatment for depression. Comorbidity with anxiety disorders and substance abuse was found equally in both subtypes of hypomania. The study suggests that recurrent brief hypomania belongs to the bipolar spectrum. The findings should be verified on larger national cohorts in other epidemiological and clinical studies.