The transmission, diagnosis, and clinical manifestations of human immunodeficiency virus (HIV) infection in children up to 13 years of age are reviewed, and maintenance and prophylactic drug therapies for these patients are discussed. HIV can be transmitted from mother to infant in utero, during delivery, or through breast milk. Perinatal transmission accounts for almost 90% of all pediatric HIV infections. HIV infection can be diagnosed with HIV culturing, polymerase chain reaction testing, the enzyme-linked immunosorbent assay, the Western blot antibody assay, or the p24 core-antigen assay. Testing should begin as soon as possible after the at-risk child reaches one month of age. CD4+ lymphocyte counts are also used in diagnosis and monitoring. The median age at diagnosis of AIDS in children with perinatally acquired HIV infection is 12-24 months. Among the many possible clinical features are Pneumocystis carinii pneumonia (PCP), cytomegalovirus infection, failure to thrive, encephalopathy, recurrent bacterial infection, thrush, lymphoid interstitial pneumonitis, lymphadenopathy, pancreatis, hepatitis, anemia, and thrombocytopenia. Zidovudine is considered the drug of choice for initial therapy in HIV-infected children and is indicated for asymptomatic infection, early symptomatic disease, and advanced disease. However, new research is questioning the role of zidovudine monotherapy. Didanosine is the only agent with FDA-approved labeling for use as second-line therapy in children who do not respond to or become resistant to zidovudine. Agents under investigation for pediatric use are zalcitabine, stavudine, lamivudine, and nevirapine. Drug combinations, such as zidovudine plus didanosine, are also being examined. Zidovudine appears to reduce the rate of maternal transmission of HIV. Agents used prophylactically against PCP in children are trimethoprim-sulfamethoxazole, dapsone, and inhaled or i.v. pentamidine. HIV-infected children should also received prophylaxis against recurrent bacterial infections. The standard pediatric immunization schedule is used, but inactivated injectable poliovirus vaccine must be given instead of the live oral vaccine. Zidovudine remains the first-line agent for treating HIV infection in children. Alternatives are available for those who do not respond to zidovudine.