Statistical modelling is applied to routine AIDS surveillance data to assess recent trends and to provide a range of short-term predictions. Several alternative functions have been fitted to half-yearly incidence data reported by the countries of the European Community by 31 December 1989 and adjusted for reporting delays. Among homosexual/bisexual men, recent trends in AIDS incidence are more nearly linear than exponential. Higher though less than exponential rates of growth are observed among intravenous drug users and among those presumed infected by heterosexual contact. Extrapolations to the end of 1991 using each of five functions provide a range of forecasts. Projections of total cumulated cases to the end of 1991 lie in the range 60,000-78,000, with 24,000-30,000 projected cases among homosexual/bisexual men, 23,000-33,000 among intravenous drug users, and 6000-8000 in the heterosexual transmission group. With the possible exception of the latter group, the lower parts of these ranges appear more probable.