The patient was a 52-year-old man who had been diagnosed as having a gastric ulcer and a duodenal ulcer by upper gastrointestinal endoscopy and received sanitization treatment for Helicobacter pylori in another hospital. He was referred to the hospital because a submucosal tumor of the stomach was detected by a follow-up examination. We performed upper gastrointestinal endoscopy again and diagnosed it as gastric malignant lymphoma by a biopsy. The patient was admitted to the hospital for the purpose of operation. Endoscopic examination of the lower digestive tract disclosed a submucosal tumor in the lower rectum and, as a result of a biopsy, it was diagnosed as rectal malignant lymphoma. On this account we performed total gastrectomy and abdominoperineal resection of rectum at the same time. As a result of histopathological examination, both the gastric and rectal lesitions were follicular lymphoma. After discharge from the hospital, he received chemotherapy in another hospital. Thereafter he has been recurrence-free. It is considered very rare that gastric malignant lymphoma coexists with rectal malignant lymphoma. In the treatment of such condition, we can attempt to perform total gastrectomy and abdominoperineal excision of recturm at the same time. And it appears to be best that chemotherapy is combined with these operative procedures to which the patient may be tolerable.