The results of a survey on AIDS conducted in Belgium, Denmark, Finland, France, FRG, Italy, the Netherlands, Norway, Sweden, Switzerland and the UK are presented. The definition of AIDS drawn up by the Centers for Disease Control, USA, was used in the survey. On the basis of the number of patients reported annually, it would appear that the disease has reached epidemic proportions in Europe. More than half of the 243 cases documented in the survey were reported during the first nine months of 1983. The most important risk factor in Europe is male homosexuality--among the 223 evaluable AIDS cases, male homosexuals constituted the largest group (58%). These patients probably contracted the disease through homosexual contacts in the USA, Europe or Haiti. Another new and important risk group has emerged in Europe in addition to male homosexuals--black persons from Central Africa (26%) and Caucasians who have had intimate contact with natives from Central Africa (3%). These patients had no known history of homosexuality or drug abuse. The fact that Caucasian patients acquired the disease in this manner suggests that AIDS is not restricted to certain ethnic groups in Central Africa. Drug abuse alone was not identified as a risk factor. The proportion of hemophiliacs and Haitians with AIDS in Europe (2%) was similar to that found in the USA (4%). The clinical presentation of the disease in the two most important groups, i.e. male homosexuals and patients from Central Africa, differed slightly. Kaposi's sarcoma was more frequent in the former group (40%) than in the latter.(ABSTRACT TRUNCATED AT 250 WORDS)