The importance of bacterial infections in children with AIDS was emphasized when they were included within the CDC classification system for children under 13 years of age infected with the HIV. The information available in Mexico on frequency, types of infections and causative agents is scarce. In this study, the frequency and microbiology of bacterial infections in children with AIDS seen at the Hospital Infantil de Mexico Federico Gomez is reported. From September 1985 to December 1991, we found 72 HIV infected children, 6 were classified P0, 6 as asymptomatic (P1) and 60 as symptomatic infections (P2). From this last group, 50 were secondarily infected with bacteria; there was a total of 129 episodes of bacterial infections, averaging 2.5 episodes per patient. Respiratory infections were the most frequent (74.41%), followed by septicemia (10.07%), skin and underlying tissue infections (6.96%) and urinary tract infections (6.17%). Infections of the CNS and deep abscesses were less frequent. Overall mortality rate was 76%, however only in 18 children (36%) was it directly attributed to the bacterial infections. Etiology was documented in 46 episodes (33.65%) of which 30 (65.31%) were gram-negative bacteria and 16 (34.78%) were gram-positive. The best possible methodology must be used for the etiologic diagnosis of bacterial infections in children with AIDS in order to select the most appropriate treatment for severe or recurrent bacterial infections.