Mantle cell lymphoma (MCL) is an aggressive B-cell lymphoma that makes up about 2.5% of non-Hodgkin lymphomas in the US. It usually presents in the 5th and 6th decades of life at advanced stages with generalized lymphadenopathy and bone marrow involvement. Extranodal sites are frequently involved, including liver, spleen, gastrointestinal tract, Waldeyer’s ring, lung, and pleura. Gastrointestinal tract is involved in 10% to 25% of cases. It may take the form of multiple small polyps in small and large bowel (lymphomatoid polyposis), a single bulky tumor nodule, superficial ulcers, or just diffuse thickening of the mucosa. Besides MCL, lymphomatoid polyposis type presentation can also be caused by follicular lymphomas and marginal zone lymphomas of the MALT type. The presenting symptoms include abdominal pain, diarrhea, and melena. The specimen in this photograph shows a single bulky 6.0 cm mass involving the duodenum. The patient presented with severe abdominal pain and vomiting. The histologic and immunohistochemical features were classic for mantle cell lymphoma.