A retrospective study of 12 cases of so called histiocytosis-X and 3 cases of malignant histiocytosis was done. It was possible to establish the differences in clinical, morphologic and cytochemical findings of both diseases. The diagnosis of histiocytosis-X can be confirmed by multinucleated histiocytes interrupted by eosinophils and plasmacells. The histopathology of malignant histiocytosis is different and is characterized by atypical histiocytes. Erythrophagocytosis throughout the tissues is seen. Typical histochemistry (acid phosphatase and naphtol-AS-acetat-esterase) findings are also helpful for diagnosis. The treatment of both diseases should be continued at least six months after disappearance of clinical apparent lesions. Combination chemotherapy with vinblastine and prednisone is suggested. In cases of histiocytosis-X in isolated lesions curettage or irradiation may be adequate. Long term remissions and presumed cures of histiocytosis-X are possible in over 70% of the cases. A strict correlation between the prognosis and the degree of involvement is confirmed. Even in cases of malignant histiocytosis, previously reported as rapidly fatal disease, combination chemotherapy may produce complete long term remissions.
