A 52-year-old man was admitted to our hospital in October 2001 with abdominal pain. Abdominal X-ray indicated a diagnosis of ileus. Histopathological and immunological examination resulted in a diagnosis of immunoproliferative small intestinal disease (IPSID). He was treated with THP-COP therapy (pirarubicin, cyclophosphamide, vincristine, and prednisolone), which resulted in complete remission. Outpatient follow-up revealed hypoalbuminemia in May 2003 and upper gastrointestinal endoscopy showed duodenal mucosal nodularity. He was diagnosed with relapsed IPSID and salvage chemotherapy was started. Follow-up endoscopy confirmed that the therapy was effective, but uncovered another duodenal mucosal nodularity. Immunohistochemical staining revealed T-cell lymphoma. Chemotherapy was discontinued and the patient died in December 2004.