ObjectiveMonitoring HIV infection in sentinel populations of sexually transmitted disease (STD) patients in several geographical areas. This paper describes the main characteristics of the study populations and compares HIV seropositivity rates within and between networks in different subgroups: homo-/bisexuals, intravenous drug users (IVDU) and non-IVDU heterosexuals.DesignHIV testing is performed with informed consent in most networks. It is mandatory for STD patients in Hungary, while the English and Welsh, Scottish and French networks use unlinked anonymous testing.SettingEighteen networks in 17 European countries are participating in the study. The networks usually consist of STD or dermato-venereology clinics.PatientsPatients presenting at any of the clinic sites with a new episode of one or more of a selected list of 12 STD were eligible for the study. This study recorded a total of 36827 STD episodes, registered between June 1990 and December 1991. HIV test results were known for 33004 (89.6%) of the patients.ResultsHIV seropositivity rates were usually much higher for the homo-/bisexual and IVDU patients than for the non-IVDU heterosexuals. However, HIV-seropositive patients were found among non-IVDU heterosexuals in all but the Czech network.ConclusionThis Concerted Action has successfully launched an HIV sentinel surveillance programme among STD patients in 17 European countries using a standard methodology.