BACKGROUND: Not much is known about hypomanic states in subjects free of major and minor depressive mood disorders. Our aim was to identify and characterise a group of such "pure" hypomanics in relation to a normal control group. METHODS: Data were obtained from the Swiss Zurich study, a stratified epidemiological sample of young adults from the general population, followed from age 20 to 40. "Pure" hypomania was defined as a period of increased activity and decreased need for sleep with consequences (e.g. legal trouble or reactions by others). Minor and major mood disorders were excluded. RESULTS: Twenty-three subjects were identified as pure hypomanics. They overlapped minimally with and were clearly different from subjects with DSM-IV defined hypomanic episodes, most of whom had a bipolar disorder. Pure hypomanics were characterised by physical and social overactivity, elevated and irritable mood, as well as increases in extraversion, sexual interest, and risk-taking behaviors. They had higher monthly incomes and were more often married than controls. Subjective distress due to hypomanic symptoms was virtually absent. Quality of life and treatment rates for mood and anxiety were not different from controls, although sleep disturbances, substance abuse and binge eating were more frequent. LIMITATIONS: The subsample identified was small. Due to the focus of the study on pathology, some positive aspects of hypomania may have been missed. CONCLUSIONS: The existence of a group of pure hypomanics presenting a mixed picture of clinically relevant and irrelevant characteristics supports the concept of a continuum from normal to pathological mood states.