Carcinoembryonic antigen (CEA) is an important tool in the management of colorectal cancer. Its use as a prognostic indicator in resectable disease remains controversial but may be improved with molecular detection of the antigen. In monitoring patients after resection, CEA can be the first sign of a potentially curable recurrence. It can also be useful in assessing tumor response in patients being treated for metastases without easily measurable disease. CEA alone cannot dictate the type or duration of treatment but may be used in addition to standard monitoring tests.