The most common presentation of colorectal carcinoma is in the symptomatic patient, most often with complaints of rectal bleeding, abdominal pain, or change in bowel habits. Symptomatic patients often have advanced disease and, because surgical resection is the only effective therapy at present, their chance for cure is poor. Until effective treatment is available, therefore, we must identify patients at high risk for lifelong screening. In addition, more effective means of surveillance of the general population need to be developed in order to diagnose patients at risk for sporadic colorectal cancer, given that this represents the majority of patients with disease. Tumor markers also would be useful to find residual disease while it is still resectable in patients who have undergone surgery for curative resection.