The appropriate use of plasma carcinoembryonic antigen (CEA) levels in the management of patients with colorectal cancer has been debated over the last 30 years. It is clear from the very low sensitivity of this test in normal populations that there is no role for CEA assessment as a screening tool for colon cancer. Although in patients receiving chemotherapy for metastatic colon cancer, elevations of CEA generally indicate disease progression, while decreases are indicative of improvement, there is no convincing evidence that CEA monitoring significantly affects either survival or quality of life. The area of most interest for CEA monitoring has been the potential for its use after curative resection. The purpose of postoperative CEA monitoring would be to detect recurrence of cancer at an early, surgically curable stage. There is good evidence that routine CEA monitoring postresection of colon cancer detects metastatic disease on average 5 months before routine follow-up evaluation without CEA monitoring detects recurrence. Also, studies demonstrate that some patients with recurrent cancer detected by CEA monitoring may be cured by surgical resection of metastases. However, the overall cost-effectiveness of this approach is not clear, and convincing definition of the role of postoperative CEA monitoring awaits the results of large randomized clinical trials.