Patients resected for colorectal cancer are at risk for anastomotic recurrence, for adenomatous polyps and for metachronous cancer. The present retrospective study was conducted to evaluate the incidence of neoplasms of the colon, both metachronous or recurrent, in 322 patients. They were observed and resected for colorectal cancer between 1970 and 1988, with complete staging, and all agreed to be included in a follow-up program (median followup: 105 months). All the patients were submitted to colonoscopy once yearly for the first 5 years and then every 2 years. Anastomotic recurrence was observed in 22 of the 253 patients who underwent resection for rectal or sigmoid adenocarcinoma (8.7%). Sixteen of these patients were submitted to a second curative resection with a median survival of 35 months; the median survival was 6 months in the 6 patients who could not undergo this operation (p=0.0018). Metachronous adenomas of the residual colon were found in 24 patients and metachronous cancers in 5 at Stage A, according to Dukes' classification. In conclusion, a regular colonoscopic surveillance in patients resected for colorectal cancer is justified for early detection and potential resection of anastomotic recurrences, new primary cancer and adenomatous polyps. In patients resected for rectal or sigmoid carcinoma, a sigmoidoscopy should be performed every 6 months for the first 2 years for the early detection of anastomotic recurrences. In all cases, a colonoscopy should be performed every 5 years after surgery to detect metachronous lesions. Before surgery, a "clean colon" should always be established to detect possible synchronous lesions.