Multiple lymphomatous polyposis (MLP) is an uncommon type of primary non-Hodgkin's gastrointestinal B cell-lymphoma characterized by the presence of multiple lymphomatous polyps along the gastrointestinal tract. Unlike MALT-lymphoma, MLP has a strong tendency for histologically monomorphic character, extra-digestive localization, rare lymphoepithelial lesion and poor prognosis. The malignant cells of MLP share morphological, immunohistologic and cytogenetic similarities with cells of node-based mantle cell lymphoma. We report a case of mantle cell lymphoma presenting with MLP involving various segments of the gastrointestinal tract, skeletal muscles of the right thigh and bone marrow observed in a 71-year-old woman who complained of lower abdominal pain and a palpable right thigh mass. (Korean J Gastrointest Endosc 2003;27:1520)