A 66-year-old male patient with a thyroid and nasopharyngeal cancer history visited our hospital because of a positive fecal occult blood test. Total colonoscopy detected sessile or subpedunculated polyps in the ascending colon, sigmoid colon, and rectum. These polyps were endoscopically resected, and the rectal polyp was pathologically diagnosed as adenocarcinoma in adenoma and the others as adenomas. Additionally, multiple sessile lesions were revealed in the sigmoid colon and rectum. A complete gastrointestinal tract examination revealed multiple foci of glycogenic acanthosis in the esophagus, multiple sessile lesions in the stomach, multiple sessile lesions, clubbings (rod-shaped lesions), and venous malformations in the small bowel. Mucocutaneous examination indicated hemangiomas on the body trunk, patchy pigmentation on the glans penis, and keratotic papules in the inguinal region. The National Comprehensive Cancer Network diagnostic criteria for Cowden syndrome were used in this case. The patient met four major and two minor criteria;thus, Cowden syndrome was diagnosed. Moreover, the patient was had phosphatase and tensin homolog deleted on chromosome 10 gene mutation. This is the first reported case of metachronal triple cancers in a male patient with Cowden syndrome, and our results indicate the importance of cancer surveillance.