A middle-aged man with lymphocytic lymphoma had numerous sea-blue histiocytes in his bone marrow, splenomegaly and thrombocytopenia. Thus, his illness mimicked that of patients with the primary syndrome of the sea-blue histiocyte. However, the paucity of sea-blue histiocytes in his spleen, the absence of neurologic disease, his age and the ultrastructure of his abnormal histiocytes were all evidence for the presence of the acquired syndrome. The pathogenesis of sea-blue histiocytosis and the relationship between acquired cases and the primary syndrome are discussed.