We report a case of multiple primary tumors pointed out during 11 years after operation for breast cancer in a 57-year-old woman. The patient had been operated on for Lt. breast cancer at the age of 46, gastric cancer at 47, and brain tumor at 51. Thereafter she had been followed until 57 years of age, when a chest X-ray film showed an abnormal lung shadow. With a diagnossis of metastatic lung cancer, the tumor was resected. It was found that the lung tumor was originated from neither breast nor stomach cancer, but from cancer of the sigmoid colon which newly occured. In obserbation of clinical course after surgery for a malignancy, we must always entertain probable ma-lignancies in other organs.