The clinical, histologic, and immunologic features of three cases of lymphoma presenting with gastrointestinal symptoms and involving the gastrointestinal tract were studied. Two of the cases had involvement of long segments of the bowel with polypoid lesions, a rare presentation of gastrointestinal lymphoma referred to as multiple lymphomatous polyposis (MLP). All cases were classified as mantle-zone lymphoma (MZL), a follicular variant of intermediate lymphocytic lymphoma (ILL) characterized by the proliferation of small atypical lymphoid cells as wide mantles surrounding benign-appearing germinal centers. The patients were typical of other patients with MZL in that they were male, middle age or older, and their clinical courses were not aggressive despite the presence of disease at an advanced stage. Our review of the literature suggests that there is an inordinate number of cases of MZL with gastrointestinal involvement. We also note that most reports of cases of MLP have described histologic lesions remarkably similar to what we have observed. We conclude that MZL may have predilection for involvement of the gastrointestinal tract, that this involvement is often in the manner of MLP, and that most cases of MLP probably have MZL or ILL.