The bone marrow of 20 autopsy cases of patients with Acquired Immune Deficiency Syndrome was examined. The study suggests that the bone marrow changes are frequent and of diagnostic value to recognize the syndrome. It is assumed that there is a diagnostic lesional pattern in which the following elements are predominant: hypercellularity, absent or reduced granulopoiesis, plasmocytosis, histiocytosis and megakariocytic dysplasia.