As of December 1986, we have identified 23 symptomatic children with human immunodeficiency virus (HIV) infection in New Haven. Twelve developed AIDS as manifested by lymphocytic interstitial pneumonitis, Pneumocystis carinii pneumonia (PCP), and/or disseminated mycobacterial infections; seven of them have died. The remainder have milder clinical syndromes, which include failure to thrive, diffuse lymphadenopathy, and parotid swelling. When compared to adults with AIDS, children often have hypergammaglobulinemia and normal numbers of T4 lymphocytes. Intravenous drug abuse by the mother or mother's consort is the risk factor in 87 percent of these children. Two families have now been identified with more than one symptomatic child, but in no family is there evidence of spread from symptomatic children to uninfected siblings. A prospective study was begun to attempt to assess the risk of developing symptomatic HIV infection when a child is born to a mother with antibodies to HIV.