A 55-year-old man suffering from gastric cancer associated with metastases to the lymph node, gallbladder, and liver was administered chemotherapy with S-1 and cisplatin. Before initiation of therapy, the primary tumor, lymph node metastases, and liver metastases showed fluorodeoxyglucose (FDG) accumulation by positron emission tomography (PET). After 1 course of chemotherapy, the patient received curative surgical treatment including distal gastrectomy, partial hepatectomy, cholecystectomy, and lymph node dissection. The final pathological finding was moderately differentiated adenocarcinoma, T4b(SI), N3a(10/20), P0, CY0, pH1, pM1, Stage IV. Five months after surgery, the serum carcinoembryonic antigen (CEA) level was found to be increasing and PET examination identified an FDG-accumulating nodule in the ascending colon. Colonoscopy identified a submucosal tumor diagnosed as a metastasis from the gastric cancer. Right colectomy was performed 7 months after the first surgery resulting in a curative resection. In each surgery, PET examination indicated that no other distant metastases existed, and curative resection would be possible. Furthermore, although solitary metastatic colorectal lesions are rare, PET examination revealed them accurately. Thus, FDG-PET is very useful for identifying metastases in patients with gastric cancer.