The case of a 44-year-old man diagnosed of a true histiocytic lymphoma who, after autologous bone marrow transplantation, developed leukemia with histiocytic cells is reported. Morphologic, cytochemical, immunophenotypic and genotypic characteristics of malignant cells are described, and the literature about this and related entities is reviewed. In addition, comparison with a recent report of malignant histiocytosis with leukemic involvement is established and its inclusion in the recently proposed subtype of monocytic leukemia with histiocytic differentiation (M5c), suggested.