Four patients, aged 46, 61, 22, and 73 years, were studied for their fatal disease characterized by fever, cutaneous infiltrate, pruritus, generalized lymphadenopathy, hepatosplenomegaly, and eosinophilia. Pathologically, there was a systemic proliferation of non-phagocytic immature histiocytes in various organs in every patient. Their clinical courses lasted 7, 21, 36, and 6 months, respectively. Their disease process shared certain clinical and pathologic features with malignant histiocytosis, reported as histiocytic medullary reticulosis, and leukemic reticuloendotheliosis, and partly with histiocytosis X. It is best classified as a variant of malignant histiocytosis.