OBJECTIVE:To describe a complication of oral vaccination with live, attenuated poliomyelitis virus in a child infected with HIV. DESIGN:Case report. SETTING:Teaching hospital in Harare, Zimbabwe. SUBJECTS:A boy of 41/2 years and his mother. MAIN OUTCOME MEASURES:Results of clinical and laboratory investigations. RESULTS:Two weeks after receiving the second dose of oral poliomyelitis vaccine during national immunisation days the child developed paralysis of the right leg. He had a high titre of antibodies against poliovirus type 2, as well as antibodies against HIV-1, a low CD4 count, a ratio of CD4 to CD8 count of 0.47, and hypergammaglobulinaemia. He did not have any antibodies against diphtheria, tetanus, or poliovirus types 1 and 3, although he had been given diphtheria, tetanus, and pertussis and oral polio vaccines during his first year and a booster of the diphtheria, tetanus, and pertussis vaccine at 24 months. He had no clinical symptoms of AIDS, but his mother had AIDS and tuberculosis. CONCLUSION:Paralytic poliomyelitis in this child with HIV infection was caused by poliovirus type 2 after oral poliomyelitis vaccine.