We reviewed 2110 bone marrow aspirations from the same number of patients to establish the incidence and associations of peripheral and bone marrow basophilia. Of these, 125 cases of marrow basophilia (5.9% incidence) and 63 cases of peripheral basophilia (3.0% incidence) were identified. There were 33 patients with simultaneous marrow and peripheral basophilia, which was only significantly associated with chronic myelogenous leukemia (24 cases). Isolated peripheral basophilia was rarely seen (30 patients, 1.4% incidence) and it did not reflect any significant pathologic association. Marrow basophilia was significantly present in chronic myeloproliferative disorders, idiopathic myelodysplasia, certain erythrocyte disorders, such as iron deficiency anemia, and aplastic anemia. The incidence of marrow basophilia in patients with lymphoma, acute leukemia, or solid carcinoma was not significantly different from what it would be as a chance occurrence. Our findings suggest that marrow basophilia is a specific, but not sensitive, marker of myeloproliferative and dysmyelopoietic syndromes.