Opportunistic diseases (OD) are the most common cause of death in AIDS patients. To access the incidence of OD and survival in advanced immunodeficiency, we included 79 patients with AIDS treated at Hospital Evandro Chagas (FIOCRUZ) from September 1997 to December 1999 with at least one CD4 count <or=100 cells/mm(3). The incidence of OD was analyzed by Poisson's regression, and survival by Kaplan Meier and Cox analysis, considering a retrospective (before CD4 <or=100 cells/mm(3)) and a prospective (after CD4 <or=100 cells/mm(3)) period, and controlling for demographic, clinical and laboratory characteristics. The confidence interval estipulated was 95%. Mean follow-up period was 733 days (CI = 683-782). During the study 9 (11.4%) patients died. Survival from AIDS diagnosis was a mean of 2589 days (CI = 2363-2816) and from the date of the CD4 count CD4 <or=100 cells/mm(3) was a mean of 1376 (CI = 1181-1572) days. Incidence of OD was 0.51 pp/y before CD4 <or= 100 cells/mm(3) and 0.29 pp/y after CD4 <or= 100 cells/mm(3). A lower number of ODs before CD4 < 100 cells/mm(3) was associated with lower incidence rates after CD4 <or= 100 cells/mm(3). AIDS diagnosis based on CD4+ counts <or= 200 cells/mm(3) was associated with lower incidence rates after CD4 <or= 100 cells/mm(3). Baseline CD4 counts above 50 cells/mm(3) (HR = 0.13) and restoration of baseline CD4+ counts above 100 cells/mm(3) (HR = 0.16) were associated with a lower risk of death. Controlling both variables, only restoration of baseline counts was statistically significant (HR = 0.22, p = 0.04). We found a very low incidence of OD and long survival after CD4 < 100 cells/mm(3). Survival was significantly associated with restoration of baseline CD4 counts above 100 cells/mm(3).