The authors describe a patient with malignant lymphoma presenting with clinically severe malabsorption due to diffuse involvement of the small intestine and with intestinal obstruction. The histologic diagnosis was based on the association of (1) diffuse involvement of the small intestine showing lymphoid tissue expansion and (2) a non-classified form of highly malignant lymphoma. After surgical resection of a stenotic part of the small intestine, abdominal irradiation therapy was done, and the patient improved.