Three hundred forty-five colorectal cancers were identified in 320 patients over a nine-year period. Twenty-one patients (7 percent) had synchronous cancers. Metachronous cancers were identified in five patients (2 percent). Thirteen of the synchronous cancers were foci of invasive adenocarcinoma in polyps with elements of benign neoplastic tissue. There was a trend for younger patients to have multiple colon cancers. Fifteen percent of the synchronous colon cancer patients were less than 50 years of age. The mean age of patients who presented with metachronous cancer was 54, and 11 years was the average time interval between the diagnosis of the initial and the metachronous tumor. Colonoscopy proved to be more reliable than barium-enema examinations in identifying synchronous cancers. It is concluded from this review that before elective resections, colonoscopy should be used to effectively screen patients for synchronous cancers, and following curative resection, the residual colon should be periodically examined for the remainder of the patient's life.