A 72-year-old woman underwent a low anterior resection of the rectum and a total hysterectomy with a bilateral salpingo- oophorectomy simultaneously for rectal and ovarian cancer, respectively. The pathological diagnosis was a moderately differentiated adenocarcinoma of the rectum with some poorly differentiated components signet-ring cell components. A mucinous adenocarcinoma, with similar characteristics as that in the rectum, was found in the ovary. Intraoperative findings revealed no direct invasion between the rectum and ovaries, with no peritoneal dissemination. She was, therefore, diagnosed with synchronous double cancer. The rectal cancer was pT3N0M0, Stage Ⅱ and the ovarian cancer pStage Ⅰ. Adjuvant chemotherapy with capecitabine was performed for high-risk Stage Ⅱ rectal cancer. At 3.5 years after surgery, her CA19-9 level was high and pleural dissemination and para-aortic lymph node metastasis were confirmed on thoracoabdominal CT. Twelve years after the gastrectomy for gastric cancer, a comparison of the pathological specimens of her stomach at that time with the current pathological specimens revealed that the rectal and ovarian tumors were metastases of gastric cancer and that the current recurrence was a late recurrence of this disease. Late recurrence after gastrectomy, especially 10 years or more after surgery, is extremely rare.