Antibody to acquired immunodeficiency syndrome (AIDS)-associated retroviruses (ARVs) was investigated in 68 pediatric patients with abnormalities of T-cell and/or B-cell immunity. All except seven patients conformed to a specific World Health Organization classification for immunodeficiency disease. These seven patients had polyclonal hypergammaglobulinemia and T-cell immunodeficiency. Six of the seven patients had antibody to ARV and had risk factors associated with AIDS. The one patient without antiviral antibody had no AIDS risk factors. No antibody was detected in 61 patients with other primary immunodeficiency disorders. We conclude that ARV first appeared in our population of immunodeficient pediatric patients prior to 1978, is associated with a distinctive immunologic phenotype consisting of polyclonal hypergammaglobulinemia and T-cell immunodeficiency, and does not appear as an opportunistic infection in other immunodeficiency disorders. Detection of the retrovirus associated with AIDS is of value in identifying infants and children who may have unique medical and social problems that occur with AIDS.