A 71-year-old male underwent an upper gastrointestinal endoscopy ; as a result of a biopsy, extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) was suspected. Abdominal computed tomography scan disclosed an approximately 4-cm-large mass in the ileocecal region. After ileocecal resection, the patient was diagnosed with MALT lymphoma (CD79a⁺, CD20⁺, CD3^-, CD5^-, CD10^-, and cyclin D1^-). He achieved complete remission after receiving chemotherapy. However, four years after the primary onset, he was diagnosed with recurrence. Although he achieved remission again by salvage therapy, six years after the primary onset, he was referred to our hospital with second recurrence. Colonoscopy revealed the appearance of multiple lymphomatous polyposis and biopsy specimens showed monotonous proliferation of centrocyte-like cells (CD79a⁺, CD20⁺, CD3^-, CD5^-, CD10^-, and cyclin D1⁺), which were consistent with mantle cell lymphoma (MCL) except for CD5. The result of reactivity to cyclin D1 was different from that at initial diagnosis, so we reexamined the initial surgical specimens, the histological and histochemical features of which were proven to be the same as those of colonic biopsy specimens. Finally, the patient was diagnosed with CD5-negative MCL (marginal zone-like variant). As MALT lymphoma and MCL sometimes show similar histological features, they are difficult to distinguish from each other. It is necessary to take the possibility of this rare phenotype of MCL into consideration and to reexamine the initial diagnosis, especially if the clinical course is unusual for MALT lymphoma. This case is very interesting in view of its indolent clinical feature and phenotype. [J Clin Exp Hematopathol 52(3) : 185-191, 2012]