Lymphomatous polyposis of the gastrointestinal tract is rare. It refers to a heterogeneous group of small B-cell lymphomas including mantle cell lymphoma, follicular lymphoma and MALT lymphoma. It is characterized by the presence of multiple lymphomatous polyps along one or more segments of the digestive tract. Clinical symptoms are non-specific. We herein report the case of a 74-year old man initially admitted for an upper and lower gastrointestinal endoscopy to explore a positive Hemoccult^® test. The endoscopy revealed multiple polyps all along the gastrointestinal tract. Histopathological study showed a diffuse lymphomatous proliferation of small B-cells whose immunohistochemical features were compatible with a mantle cell lymphoma. Tumoral B-cells showed a positivity of cyclin D1 markers but negativity for CD5. Immunochemotherapy with R-CHOP (rituximab, cyclophosphamide, adriamycine, vincristine and prednisone) was initiated. Based on this case study, the pitfalls of gastrointestinal tract lymphomatous polyposis diagnosis, prognosis and treatment options are discussed.