When considering screening for colorectal cancer, doctors should evaluate patient risk. For patients at average risk for colorectal cancer, doctors should recommend screening starting at age 50 years. Patients with a parent, sibling, or child with colorectal cancer should begin screening at 40 years or 10 years younger than the age at diagnosis of the patient's youngest affected relative (whichever is younger). Tests appropriate for screening average-risk patients include stool-based tests, flexible sigmoidoscopy, or optical colonoscopy. Patient preference and availability and adverse effects of the tests should guide choice. High-risk patients should get optical colonoscopy. Doctors should not recommend colorectal cancer screening for patients older than 75 years or patients who are likely to die within 10 years.