A patient with tumor-stage mycosis fungoides and lymph node involvement had sea-blue (ceroid-containing) histiocytes in her bone marrow. Leukopenia, eosinophilia, and a mild type II beta-hyperlipoproteinemia were also features. Sea-blue histiocytes were demonstrated in the skin after the mycosis fungoides infiltrate had cleared with treatment. There is a possible interrelationship between the sea-blue histiocytes, the abnormal mycosis cells in the skin, and lipid metabolism.