Familial adenomatous polyposis is an autosomal dominant hereditary disease leading to the development of numerous colorectal polyps with malignant potential. Extra-colonic neoplasms are observed often in patients with familial adenomatous polyposis, but clinical characteristics of gastric cancer associated with familial adenomatous polyposis are not well understood. We studied the clinical characteristics of five Japanese patients who developed gastric cancer after undergoing colectomy for familial adenomatous polyposis. Gastric cancer was found on gastroduodenal endoscopy performed during postoperative follow-up in all five patients. Mean ages at the time of colectomy and at the time of diagnosis of gastric cancer were 39.2 and 58 years, respectively. Importantly, gastric fundic gland polyps were undetectable in these five patients. The mean duration between colectomy and diagnosis of gastric cancer was more than 20 years in three of five patients (mean: 19 years and 1 month). Cancers were multiple in three of five patients. Two patients developed metachronous gastric cancer in the gastric remnant. All five patients presented with well to moderately differentiated adenocarcinoma; four of the five patients were stage IA. Characteristics of the gastric cancer with familial adenomatous polyposis include a long duration between occurrence of gastric cancer and colectomy, metachronous cancers, multicentric lesions, and a high rate of well to moderately differentiated adenocarcinoma. Long-term and periodic gastroduodenal surveillance endoscopy is recommended for patients with FAP who underwent colectomy.