The clinical and immunologic abnormalities of 7 infants with Lymphadenopathy Associated Virus (LAV) infection are reported. Indicative immune changes, positive anti-LAV serologic test and/or virus isolation led to the diagnosis. In a case with a particularly severe form of the disease, whose mother died from AIDS, serologic tests and virus isolation were negative. Beside a case associated with blood transfusion, the familial and ethnic context helped the diagnosis. Clinical and biochemical features were close to those in adult AIDS, including hepatosplenomegaly, polyadenopathy, a decreased absolute number of OKT4(+) lymphocytes and hypergammaglobulinemia. The importance of cellular and sometimes also humoral immune deficiency was highly variable. For 4 patients, the severity of the immune deficiency allowed the diagnosis of AIDS. Occurrence of such an infection in the first months of life suggests a fetomaternal viral transmission; however, a postnatal contamination cannot be ruled out. Long-term prognosis is difficult to assess. It depends, among other factors, on the importance of the immune deficiency.