BACKGROUND Carcinoembryonic antigen (CEA) is one of the most widely used tumor markers worldwide. Its main application is mostly in gastrointestinal cancers, especially in colorectal malignancy. Although in use for almost 30 years, the clinical value of CEA in colorectal cancer is still not clear. METHODS The literature relevant to the clinical value of CEA in colorectal cancer was reviewed. Particular attention was paid to studies involving metaanalyses and guidelines issued by Expert Panels. RESULTS Although of little use in detecting early colorectal cancer, high preoperative concentrations of CEA correlate with adverse prognosis. Serial CEA measurements can detect recurrent colorectal cancer with a sensitivity of approximately 80%, a specificity of approximately 70%, and can provide a lead time of approximately 5 months. CEA is the most frequent indicator of recurrence in asymptomatic patients and currently is the most cost-effective test for the preclinical detection of resectable disease. CEA is most useful for the early detection of liver metastasis in patients with diagnosed colorectal cancer. Overall, however, little evidence is available that monitoring of all patients with diagnosed colorectal cancer leads to enhanced patient outcome or quality of life. CONCLUSIONS Currently, the most useful application of CEA is in the detection of liver metastasis from colorectal cancers. Because of the relative success of surgery in resecting hepatic metastases, serial determinations of the marker are recommended for detecting cancer spread to the liver. In the future, preoperative concentrations of CEA may be included with the standard staging procedures for assessing prognosis.