From the beginning of the AIDS epidemic, pneumocystis pneumonia (PCP) has been distinguished as one of the most frequent opportunistic diseases with high morbid-mortality. As from 1996, the advent of the highly active antiretroviral therapy (HAART) has changed the characteristics of such epidemic by reducing its related diseases and, as a result, AIDS-related mortality. With the purpose to estimate PCP occurrence and HAART interference, 376 HIV-infected or AIDS patients were studied from January 1992 to December 2002. Among them, 58 (15.5%) PCP cases were found. There was a higher occurrence of PCP in the group of patients in which HAART was not used, with 40 (69.0%) of the episodes. As regards the studied period, a tendency to a linear reduction in annual PCP incidence was observed. The mean of T CD4+ lymphocytes in the patients with PCP (117 cells/mm3) was significantly lower when compared to that of the other individuals (325 cells/mm3). Therefore, this study suggests a temporal reduction in PCP occurrence related to HAART use with higher T CD4+ lymphocyte counts. Nevertheless, this opportunistic infection still shows significant incidence in AIDS patients.