A retrospective review of 1888 colorectal cancer patients demonstrated 37 metachronous cancers in 30 patients for a metachronous cancer rate of 1.6 percent. Evaluation of the index cancers consisted of the traditional single-contrast barium enema and proctoscopic evaluation. Forty percent of the metachronous cancers appeared within two years of the index cancer. If the minimum length of the polyp-cancer sequence is three to five years, then this represents a failure of a traditional preoperative evaluation. A more sensitive evaluation potentially could decrease the metachronous cancer rate. Colonoscopy, which has been found to be more accurate in detecting synchronous neoplasms, should be included in the evaluation of all patients with colorectal cancers.