Of 6,988 bone marrow biopsies seen from 1973 to 1986, granulomas were identified in 72 specimens. In this period, biopsies doubled, but the yearly incidence of granulomas increased from 0.3% to 2.2%. The granulomas were associated with infectious disease (30%), hematologic disorders (25%), sarcoidosis (11%), nonhematologic malignancies (10%), drug reaction (5%), other diseases (6%), and no final diagnosis (6%). In contrast to studies reporting a high incidence of tuberculosis and histoplasmosis, we found incidences of 6% and 4%, respectively. The proportion of hematologic disorders was constant from 1973 to 1986, while the rate of infectious disease increased from 19% in 1973-1979 to 32% in 1980-1986. The incidence of sarcoidosis dropped from 32% to 3%. Patients with fever of unknown origin were 15 times more likely to have marrow granulomas than patients biopsied for other reasons. We have documented an increase in the incidence of marrow granulomas with a corresponding change in the clinical profile. Some possible new disease and drug associations have been identified.