We encountered a 46-year-old woman with synchronous quintuple primary cancers. She did not present with any symptoms, and her tumors were discovered at a gynecological screening. She had clear cell adenocarcinoma of the right ovary, moderately differentiated endometrioid adenocarcinoma of the endometrium, moderately differentiated adenocarcinoma of the ascending colon, well-differentiated adenocarcinoma of the rectum, and poorly differentiated papillary adenocarcinoma of the left lung. A fluorodeoxyglucose-positron emission tomography and other imaging techniques were extremely useful for the diagnosis of multiple primary cancers. Moreover, MSH2 protein expression was absent in the tumors of the ovary, endometrium, ascending colon, and rectum, while the rectal cancer also lacked MLH1 protein. These findings suggested that an abnormality of DNA mismatch repair genes was responsible for carcinogenesis.