A case of radiation-induced rectal cancer is presented. In November, 1971, a 58-year-old woman had a stage II squamous cell carcinoma in the uterine cervix. She underwent a hysterectomy and postoperative radiotherapy. External pelvic irradiation of 10 MV x-ray was carried out in 15 fractions of 2 Gy daily, with a total dose of 30 Gy, and intracavitary radium insertion with a total dose of 960 mg hours (20 mg x 48 hours). She had been followed-up in our department since 1972, when rectal bleeding occurred. Proctoscopy and periodical biopsies were performed when the patient visited our hospital. There was no evidence of malignant tumor cells nor of recurrent cervical cancer from 1973 to 1989. In August, 1990, a biopsy specimen taken from a rectal ulcer revealed a malignant mucinous adenocarcinoma. The time interval between the radiotherapy and the development of the rectal cancer was 19 years. Microscopically, the main lesion was situated in the granulation tissue covered with the regenerating mucosal epithelium, and histologically was found to be a mucinous adenocarcinoma. Other radiation damage was additionally found including colitis, endarteritis and intestinal wall fibrosis. The evidence strongly suggested the present case to be one of radiation-induced rectal cancer.