The abscopal effect is characterized by the spontaneous regression of unirradiated tumors resulting from the effect of irradiation on remote tissue. We report a case of NK/T-cell lymphoma of the small intestine that achieved complete remission as a result of an abscopal effect. A 74-year-old Japanese woman was referred to our hospital because of ileus and suspected perforation of the gastrointestinal tract. An emergency operation was performed and a perforated ulcerative tumor in the small intestine and enlarged mesenteric lymph nodes were found. Histopathological examination of the resected small bowel showed infiltration of large lymphoid cells with irregular nuclei and they were positive for CD3, CD56, TIA-1 and granzyme B. Physical examination did not reveal any lymphadenopathy in the neck, axillary or inguinal regions, skin involvement or nasal infiltration. The CT scans revealed multiple tumors in her upper abdomen and an obstructing conglomerate of small intestinal tumors. The patient did not show any response to CHOP therapy and radiotherapy was delivered to the lower abdominal field for the treatment of the ileus at a total dose of 44 Gy. Two months after radiotherapy, abdominal CT scans showed the disappearance of not only the tumors in the irradiation field but also the upper abdominal tumors that had not been irradiated. The patient has remained in complete remission for 15 months.