We report a rare case of primary gastrointestinal lymphoma, stage IE, in a 58-year-old white man who had multiple colonic polyps measuring up to 1 x 1.1 cm. The tumor originated in the marginal zone of the follicles infiltrating the interfollicular spaces. Follicular colonization was frequently seen. The mucosa was spared by the infiltrate. Morphologically, the neoplastic cells were monomorph, intermediate-sized blasts. Rare small to intermediate sized cells, some with centrocyte-like morphology, intermingled the blastic infiltrate. The neoplastic cells expressed CD20 and had a monotypic immunoglobulin of cytoplasmic IgM (kappa) on paraffin sections. Tumor cells stained negative for CD45RO, CD5, CD10, IgD, and CD23. Polymerase chain reaction revealed a clonal V-D-J rearrangement. Bcl-1 and bcl-2 rearrangement were not detected. We therefore suggest the diagnosis of primary large cell lymphoma with marginal zone growth pattern mimicking colonic adenomas.