Colorectal cancer is the second leading cause of cancer mortality in the United States, with more than 57 000 deaths expected in 2001 (1). Evidence from several studies suggests that screening for, detecting, and removing colorectal cancer and precancerous adenomatous polyps can reduce the incidence of colorectal cancer and colorectal cancer–related mortality (2). Questions remain, however, about which method or methods of screening should be used, how frequently screening should be performed, and at what ages screening should begin and end. In addition, health care policymakers wish to know not only whether screening is effective but also whether it is cost-effective. Existing clinical trials of colorectal cancer screening have not directly compared different screening approaches and have not tested different starting and stopping ages. In the absence of such data, cost-effectiveness analyses using simulation models may provide the best information for answering such questions (3).