See "American College of Gastroenterology Guidelines for Colorectal Cancer Screening 2008" pages 3 and 4: http://s3.gi.org/physicians/guidelines/CCSJournalPubli

See "American College of Gastroenterology Guidelines for Colorectal Cancer Screening 2008" pages 3 and 4: http://s3.gi.org/physicians/guidelines/CCSJournalPublicationFebruary2009.pdf http://s3.gi.org/physicians/guidelines/CCSJournalPublication... Summary: Usually age 50, but age 45 if you're African American. If you have a family history of the disease, then maybe screening at age 40, or 10 years younger than age at diagnosis of the youngest affected relative. With positive genetic tests for certain cancers, screening age may be 20.