Malignant tumors of the small bowel are rarely seen and are usually diagnosed in advanced stages because of the difficulties in diagnosis. Lymphomas account for %1 of malignant gastrointestinal system tumors. Primary gastrointestinal lymphoma is very rare and its preoperative diagnosis is difficult. Its diagnosis is usually made through laparotomy. A 77-year-old male patient developed acute abdomen during observation for partial mechanic intestinal obstruction. Emergent explorative laparotomy revealed perforation of a small bowel tumor. A wide small bowel resection was performed with a double-layer end-to-end anastomosis. Histopathological examination of the surgical specimen was reported as indolent B-cell non–Hodgkin's lymphoma. It should be kept in mind that small bowel tumors can present as mechanic intestinal obstruction, resulting in delayed diagnosis.