SCOTT and Robb-Smith 1 reported four cases of histiocytic medullary reticulosis which presented a definite clinical and pathologic picture. The clinical course is one of a rapidly fatal disease characterized by high irregular fever, wasting of the body, gross splenomegaly and hepatomegaly, and moderate enlargement of the lymph nodes. These patients also develop a rapidly increasing anemia, with leucopenia and thrombocytopenia, hemorrhagic manifestations, and jaundice. Terminally, a necrotizing angina may develop. The pathologic picture shows a proliferation in the lymphoid organs of active phagocytic cells containing nuclear debris and erythrocytes. In addition to the typical histiocytic cells, so-called prohistiocytes are present, and giant forms of these occur. Areas of hemorrhage and necrosis are common. Some of the lymph nodes show compression of the follicle borders by proliferation of their centers. This picture, according to Robb-Smith and others.* is similar histologically to acute reticulosis of children, generally known as Letterer-Siwe syndrome.