Gastrointestinal (GI) tract involvement by Langerhans cell histiocytosis (LCH) is a rare condition. It is typically noted in male patients with systemic disease and is associated with both poor prognosis and high morbidity. The incidence peaks in childhood. However, a limited number of cases have been reported in adults. To further characterize this disease process, we collected 24 cases of GI tract LCH from 12 patients. The patients included 2 children (4 mo and 2.3 y) and 10 adults (40 to 77 y; mean, 58.4 y), with a female predominance (9 of 12, 75%). Both children presented with failure to thrive, bloody diarrhea, and anemia. In contrast, 5 of 10 (50%) adults were asymptomatic and the rest had unrelated symptoms. Endoscopically, the pediatric patients showed the involvement of the duodenum and multiple colonic sites. However, 8 of 10 (80%) adults presented with a solitary polyp, primarily involving the colorectum (7 of 8, 88%). The lesions ranged in size from 0.1 to 0.8 cm (mean, 0.4 cm), and were predominantly intramucosal (18 of 24, 75%) with either a marginated (14 of 24, 58%) or infiltrative (10 of 24, 42%) growth pattern. Microscopic features were similar to those of LCH found elsewhere, although some cases differed by showing prominent lymphocytes (12 of 24, 50%) rather than eosinophils and large nucleoli (2 of 24, 8%). Reactive overlying mucosal and entrapped epithelial changes (10 of 24, 42%), mucosal ulceration (3 of 24, 13%), focal necrosis (1 of 24), and multinucleated giant cells (1 of 24) were also identified. Mitotic figures were absent. On immunohistochemistry, all lesions expressed the S-100 protein and CD1a. Follow-up information was available for 11 (92%) patients ranging from 2 months to 5.3 years (mean, 1.8 y). One pediatric patient was lost to follow-up. However, the other patient developed multisystem disease and died 1 year after the initial diagnosis. Two adult patients developed cutaneous disease, 2 months and 2 years after the initial diagnosis, 1 of whom had multifocal colonic disease. On the basis of this study, GI tract LCH lesions present in both children and adults with a female predominance. Consistent with earlier reports, pediatric cases are associated with systemic disease and poor prognosis. However, in adults, LCH is typically encountered as an incidental, solitary polyp. Rare cases of systemic disease may occur and, therefore, close follow-up may be warranted.