In a case of histiocytic medullary reticulosis with protracted course and necrotic skin lesions, histological study revealed infiltration of the fat tissue by atypical reticulohistiocytic cells, areas of associated fat necrosis and vascular lesions. Autophagocytosis (phagocytosis of erythrocytes, erythroblasts, platelets, lymphoid cells, and nuclear debris) was found in biopsy specimens of the subcutaneous infiltrates, lymph nodes, and bone marrow, and in necropsy specimens of skin, iliac mesenteric lymph nodes, bone marrow, liver, spleen, and suprarenal glands. Electron microscopy of various viscera showed abnormal histiocytic cells containing multiple phagocytosed erythrocytes and other blood cells in different stages of destruction and digestion. Multi-membranous bodies also were present. Defective lysosomal degradation of intracytoplasmatic ceroids in this condition is postulated.