In the thirty-four years since Letterer (21) and twenty-five years since Siwe (44) reported the entity now known as Letterer-Siwe's disease, numerous articles on the subject have appeared in the literature (1, 5, 18, 23, 27, 28, 29, 35, 37, 38, 40, 41, 45, 48, 49, 50). There have also been many papers correlating Letterer-Siwe's disease, Hand-Schüller-Christian disease, and eosinophilic granuloma under the general designation nonlipid histiocytoses, histiocytosis-X, or reticuloendotheliosis (2, 3, 6, 9, 11, 13, 15, 23, 24, 25, 50). It is not our purpose to restate the well documented clinicopathologic relationship of the “triad” (23, 24). Instead, we shall describe an as yet unrecognized roentgen finding in the gastrointestinal tract in the acute and subacute phases of the disease. We do not believe this is simply an isolated, impractical observation. With the increasing frequency of recognition of atypical cases, both in infants and adults, in which the gastrointestinal symptoms are often prodromal (4, 8, 16, 17, 18, 22, 27, 28, 29, 33, 34, 45, 48), the roentgen examination of the upper alimentary tract may give the initial clue, leading to the performance of accepted laboratory procedures for a final and positive diagnosis. Among the eight criteria originally listed by Siwe, no mention was made of the gastrointestinal tract per se. A diagnosis based on classical skin, node, pulmonary, bone, or reticuloendothelial histopathology has been described and refined from clinical, pathological, and roentgen points of view (1, 19, 20, 23, 24, 35, 38, 41, 43, 44, 49, 50). A recent case at the University of Minnesota Hospitals was of special interest not only because of the classical findings but also because of the gastrointestinal symptoms, which chronologically antedated the typical manifestations of the disease (Case I). The illness began at two months of age with vomiting and obstructive symptoms. Later, a typical skin rash appeared over the trunk and adenopathy developed. Mononuclear infiltration of skin and marrow were found even though the nodes were negative. When the child was first seen, the problem was one of emaciation and fluid loss through vomiting and loose stools. An upper gastrointestinal examination showed marked changes in the mucosa from the level of the second portion of the duodenum through the ileum. The mucosal pattern was completely coarsened, with a pebble-like appearance (Figs. 1–3). This was interpreted as indicative of intestinal infiltration by the underlying process as well as possible mesenteric node replacement resulting in complete interference with small-intestinal physiologic processes. Postmortem findings confirmed the extensive gastrointestinal invasion. With this in mind, a patient with subacute reticuloendotheliosis (Case II) was recalled to the department for examination of the gastrointestinal tract.