ObjectivesTo evaluate the mortality pattern observed in relation to the AIDS epidemic, and to estimate the current and future demographic impact of AIDS among the population aged between 20 and 39 years in Catalonia, Spain.DesignSpain has the highest cumulative incidence rate of AIDS in Europe. One-third of Spanish AIDS cases have been consistently reported from Catalonia, an autonomous region in northeastern Spain with a population of 6 million, and with Pattern I HIV transmission. In this study data from the population-based AIDS registry and death certificates in Catalonia were used.MethodsSince 1981 AIDS data have been collected routinely from all hospitals using an active surveillance system. All causes of death are coded from death certificates (ICD-9). Mortality rates since 1981 were analysed by age and sex. To assess the relative importance of premature mortality due to AIDS, years of potential life lost (YPLL) before age 65 were used.ResultsSince 1982 there has been a continuous increase in crude mortality rates, particularly significant for men aged 20–39 years after 1986 (F < 0.001). While AIDS was the fourth most likely cause of death among people aged 20–39 years in 1988, by 1991 it was the second most likely. In 1990 AIDS contributed to 13213 YPLL (8.7%) for men and 2579 YPLL (4%) for women. During the last few years AIDS-related deaths have had the highest mortality rate progression among young adults.ConclusionAccording to the current available data, AIDS might become the leading cause of death for the population aged 20–39 years in the near future. AIDS is having an important impact on the demography of European countries with Pattern I transmission and high HIV prevalence rates.