Histiocytic medullary reticulosis, known as malignant histiocytosis, is a disorder characterized by a systemic proliferation of morphologically abnormal histiocytes with prominent erythrophagocytosis. Fever, wasting hymphadenopathy, hepatosplenomegaly and pancytopenia are the main clinical pictures. Prognosis is very poor and invariably die within several months. Authors present raiological findings of pulmonary involvement in 5 cases of histologically proven histiocytic mdedullary reticulosis. The findings are progressive interstitial, aveolar or mixed infilltrations, small amount pleural effusion, hilar and/or , hilar and/or mediastinal lymph node enlargement and cardiomeglay. Histiocytic medullary reticulosis should be borne in mind in differential diagnosis of any patient who has unexplanable above radiological findings.