Thirty-five children diagnosed of AIDS were studied in order to evaluate toxicity and efficacy of oral Zidovudine treatment (AZT), as well as to analyze the clinical, biochemical, immunological and virological evolution of HIV infection throughout the treatment. Patients (19 males and 16 females) were studied from April 1988 to May 1990 with a mean follow-up time of 13.5 months (SD = 6.7 months). The mean age of the group was 4.68 years. The means of acquisition of this disease was 71.45 vertical and 28.6% via hemo-derivatives. Tolerance has been good with the main toxicity being hematological (28.5% anemia and/or neutropenia), 23% of which required blood supplements. The presence of neurological involvement and thrombopenia were observed in the incidence of greater toxicity. No influence on weight during AXT treatment was observed and hepatosplenomegalia and adenopathies were not modified. Bacterial and opportunistic infections were observed in 97.1% and 20% of patients, respectively. Neurological evolution was irregular and the improvement observed in some patients was mild and transitory. Three patients died during the follow-up from intercurrent infectious process. A progressive increase in MCV and a tendency towards leucopenia and lymphopenia (mainly in hemo-derivative infected patients) was observed. Neither significant immunological nor virological changes were observed during the treatment (except the tendency to diminish basal hypergammaglobulinemia). The results of this study were compared to other pediatric series treated with AZT.