OBJECTIVE: The immunologic defects that occur in children with HIV infection are important tests to both diagnosis and therapeutic response. The objective of this study was to verify the immunologic abnormalities in 60 children with AIDS, in Florianópolis, Santa Catarina State, Brazil. METHODS: Serum immunoglobulin levels were determined by nephelometry and compared to a normal pattern for Brazilian children. The lymphocyte T helper (CD4+) and the lymphocyte T suppressor (CD8+) count and percentage, and the ratio between them, determined by commercial flow cytometry, were compared to a pattern for healthy children of HIV-positive mothers. RESULTS: The mean serum IgG levels was higher in the children with AIDS (p<0.005). The mean serum IgM levels was higher in the children with AIDS in the age group between 13 and 108 months (p<0.005). The CD4+ lymphocytes count was below the inferior limit of the 95% confidence interval of the median reference values to each group of age in 50 (84.7%) of the 59 determinations. The CD4+ lymphocytes percentage was much lower than the percentages of reference. The graph curve of the medians of the ratio between lymphocytes CD4+ and CD8+ to each group of age was below the fifth percentile of the graph curve of the medians of reference. CONCLUSIONS: The hypergamaglobulinemia and the lymphocyte T CD4+ count and percentage are sensitive indicators of HIV infection, observed in the present study. Immunologic evaluation of the HIV-positive children is recommended, including those younger than 18 months of age.