An EC concerted action on the assessment of AIDS/HIV prevention strategies was conducted between 1989 and 1992. The aim of this concerted action (CA) was to bring together researchers who are active in this assessment field, make an initial appraisal of the results of AIDS prevention efforts, in various population groups in Europe and develop an assessment methodology. Five areas of study were selected for the CA: the population as a whole ("general population"), men who have sexual relations with other men, intravenous drug users, migrant populations, monitoring of sexually transmitted diseases (STDs) to determine changes in behaviour. For each of these areas, a working group composed of the leading researchers in the field in Europe was constituted and commissioned by the project administration and coordination team to collate and analyse data on prevention efforts and their assessment in different countries of Europe. This review presents the main results from the groups responsible in each area in the concerted action. A number of general conclusions from the results of this concerted action are drawn.