Synchronous malignancy occurs in approximately 3–4% of colorectal cancer cases. An increased risk is seen in patients with a history of adenomatous polyps, inflammatory bowel disease, hereditary nonpolyposis colorectal cancer, and familial adenomatous polyposis. Following the discovery of one colon cancer, the entire colon is examined to exclude a second neoplasm. Long-term follow-up for metachronous neoplasms is indicated.