In this article, we evaluate the effect of the 1987 revised CDC AIDS definition on the AIDS epidemiological surveillance in Catalonia. From data collected in our population-based registry, we observed a 1.3- and a 1.6-fold increase in AIDS prevalence and incidence rates, respectively. In our setting, the new criteria appear to affect case ascertainment in male intravenous drug abusers, with extrapulmonary tuberculosis being the disease that accounts for the major increase in the identified cases. An additional effect of this case revision has been on the median survival time of AIDS patients, which will probably increase due to the use of the new definition criteria.