By the end of September 1991, more than 60,000 cases of acquired immunodeficiency syndrome (AIDS) had been reported to the World Health Organization (WHO) by 31 countries in the WHO European region. Most of the cases (58,280/60,485-96%) were recorded in western Europe, chiefly in five countries: France (16,552 cases), Italy (10,584), Spain (10,101), Germany (6,968) and the United Kingdom (5,065). From the first reports in 1981 of European cases of AIDS until 1987, AIDS spread faster in the northern and central areas than elsewhere in the European region. Since then, the spread of the epidemic has been remarkably more rapid in southern Europe, while in eastern Europe AIDS is still in an early phase. More than 70% of the cases among homosexual or bisexual men were from the northern part of Europe, while the cases among intravenous drug users (IVDUs) were concentrated in the southern European countries, principally Italy and Spain. Over time, an increasing proportion of cases was recorded among IVDUs and in heterosexuals. More than 10,000 patients in Europe were diagnosed as having Kaposi's sarcoma (KS) (14% of all AIDS cases) or non-Hodgkin's lymphoma (NHL) (3%) as the presenting clinical manifestation of AIDS. The possibility of predicting the evolution of the epidemic in Europe depends heavily on the development of unbiased monitoring systems for HIV infection in the general population (i.e. anonymous unlinked testing).