We report a rare case of advanced synchronous triple cancer of the colon. A 69-year-old man was admitted to our hospital for bloody stool. Barium enema and colon fiberscopy revealed 3 protruding lesions, 1 in the cecum, 1 in the transverse colon, and 1 in the sigmoid colon. The sigmoid lesion was resected by D3 lymphadenectomy and the cecum and transverse lesions extirpated by D2 lymphadenectomy. Histologically, all 3 tumors were moderately differentiated adenocarcinoma. The sigmoid and transverse lesions had invaded to the subserous level and the cecal lesion to the muscularis propria. No regional lymph node metastasis was seen in any of the tumors. We applied comparative genomic hybridization (CGH) to investigate carcinogeneses cytogenetically and found loss of chromosome arm 17p in all 3 lesions. p53 is located in 17p13, and this suppressor gene plays an important role in the transition from adenoma to carcinoma. Our finding is consistent with the hypothesis that multiple carcinoma of the colon develops in conjunction with the adenoma-carcinoma sequence.