Granulomas in bone marrow are an infrequent finding related to diverse disease. We reviewed 8057 bone marrow studies made over a period of 10.5 years, confirming the presence of granulomas in 40 patients. Global incidence was 0.50% and annual incidence 3.80 cases/yr. Because of the non-specificity of the morphological data, the diagnostic significance of the finding is limited, but it does serve to narrow the field of etiological possibilities. Associated disease was demonstrated in 82.5%, infectious diseases being the most common (tuberculosis, brucellosis, typhoid fever and kala-azar). Two previously unpublished entities are introduced: refractory anemia with excess blast cells (dysmyelopoietic syndrome) and malignant histiocytosis. 3 patients presented human immunodeficiency virus infection, the etiopathogenic role of this retrovirus in the generation of granulomas being unknown. The efficacy of bone marrow study in demonstrating granulomas increases if both the aspirate clot and bone cylinder are examined.