This study presents the peripheral blood and bone marrow findings in eight children with perinatally acquired HIV infection, ranging in age from 5 months to 3 years. The indications for bone marrow examination were comparable to those for adults with HIV infection and included cytopenia(s), slenomegaly, failure to thrive, and suspected tuberculosis. Thrombocytopenia was the most common indication, and platelet-associated antibodies were elevated in all patients with thrombocytopenia. The peripheral blood morphology was remarkable for the presence of plasmacytosis and eosinophilia in those patients with lymphocytic interstitial pneumonia. Five patients had trephine biopsies, and marrow cellularity was normal with normal or increased megakaryocytes in all cases. Lymphoid aggregates, also described in adult patients with acquired immunodeficiency syndrome (AIDS), were present in three of five trephine biopsies. In contrast to the adult patients, myelodysplasia was not observed in the pediatric age group. None of the eight children had malignancies or opportunistic infections that were diagnosed by bone marrow examination.