To determine the true incidence of abnormalities in bone marrow specimens from patients infected with human immunodeficiency virus (HIV) and the clinical significance of these abnormalities regarding their cause and their role in the production of hematologic complications, 216 bone marrow biopsies, aspirates, and/or imprint preparations from 178 patients who either were seropositive for HIV infection or met the Centers for Disease Control (CDC) criteria for acquired immunodeficiency syndrome (AIDS) were studied. Detailed morphologic review was performed in a blind fashion as to clinical status. Extensive clinical, therapeutic, and laboratory data were collected for each patient. Statistical analysis was performed to detect significant correlations between morphologic findings and clinical/therapeutic/laboratory features. Among the most common bone marrow findings were hypercellularity (53% of specimens), myelodysplasia (69%), evidence of reticuloendothelial (RE) iron blockade (65%), megaloblastic hematopoiesis (38%), fibrosis (20%), plasmacytosis (25%), lymphocytic aggregates (36%), and granulomas (13%). A number of statistically significant correlations between morphologic findings and clinical features were noted. No significant association was detected between any morphologic finding and therapy with a variety of drugs. In 7 of 14 (50%) patients found to have marrow involvement by malignant neoplasm, the bone marrow represented the initial site of diagnosis of the neoplasm. Most of the bone marrow abnormalities associated with HIV infection appear to be related directly to the infection or its complications and not to therapeutic intervention. In certain clinical situations, bone marrow examination continues to be useful in the management of patients infected with HIV.