From 1 January 1984 until 30 June 1986 all 517 compulsorily admitted psychiatric patients of a well-defined mixed rural-urban catchment area in Baden-Württemberg, a southern State of the German Federal Republic, were compared with all 10,232 voluntarily admitted patients. Because of the very low frequency of compulsory admissions this population can be regarded as a 'core group' of committed patients. In a logit analysis the characteristics distinguishing involuntary from voluntary patients can be reduced to three main factors: the diagnosis 'schizophrenia/paranoid disorder', 'masculine gender' and the compound indicator 'not owning a home', the latter being mainly associated with youth, masculine gender and low occupational status. The strong association of these characteristics with the criteria 'severity of disease' and 'danger to oneself and others', both pre-requisites for compulsory admission according to the laws of most countries, is discussed.