In a prospective observational study 4,485 patients from 46 clinical centres in 17 European countries were followed between April 1994 and November 1996. Information on AIDS-defining events (ADEs) were collected together with basic demographic data, treatment history and laboratory results. The centres were divided into four geographical regions (north, central, south-west and south-east) so that it was possible to identify any existing regional differences in ADEs. The regional differences that we observed included a higher risk of all forms of Mycobacterium tuberculosis infections (Tb) and wasting disease in the south-west and an increased risk of infections with the Mycobacterium avium complex (MAC) in the north. In Cox multivariable analyses, where north was used as the reference group, we observed hazard ratios of 6.87, 7.77, 2.29 and 0.16 (P < 0.05 in all cases) for pulmonary Tb, extrapulmonary Tb, wasting disease and MAC respectively in the south-west. Pneumocystis carinii pneumonia (PCP) was less commonly diagnosed in the central region (RH = 0.51, 95% CI 0 32-0.79, P = 0.003) and most common in the south-east (RH = 1.04, 95% CI 0.71-1.51, P = 0.85). Comparisons with a similar 'AIDS in Europe' study that concentrated on the early phase of the epidemic reveal that most of the regional differences that were observed in the 1980s still persist in the mid-1990s.