Sixty-two patients with metachronous colorectal malignancies who underwent surgery at the Mayo Clinic were reviewed. Fifty per cent of the patients developed a second carcinoma within 5.5 years from the time of resection of their first tumor, and the time interval for the entire group ranged from one to 23 years. Adenomas of the colon or rectum occurred in 25 of the 62 patients (40 per cent). A negative correlation was noted between the age of the patients at the time of their first operation and the time interval in years from the first to second resections. The five-year cumulative probability of survival of the 62 patients after resection of the metachronous lesions was 59 per cent. Seven of the 62 patients (11 per cent) developed a third metachronous lesion. Adequate treatment for metachronous colorectal malignancies should imply surgery with a curative intent, and after resection of a first colorectal carcinoma, lifelong, periodic, total colonic evaluation is essential.