Colorectal cancer is the third leading cause of cancer-related deaths in both men and women in the United States and is estimated to have affected 148,000 people in 2002. The cumulative lifetime risk for colon cancer is approximately 5%-6%, and this risk is influenced by hereditary and lifestyle factors. In fact, 20%-30% of all colon cancer cases have a potentially definable inherited cause, and 3%-5% of colon cancers occur in genetically defined high-risk colon cancer family syndromes. Although the genes responsible for the cases of moderate-risk colon cancer remain to be characterized, many of the genes responsible for the high-risk colon cancer cases have already been determined. These genetic discoveries have been translated into clinical practice and have led to improved risk assessment through the use of genetic testing. The introduction into clinical practice of genetic testing for the assessment of colon cancer risk has led to more effective management strategies for patients with potentially high-risk colon cancer and has presented new challenges to the clinician because of the unique issues involved with genetic testing. In this review, an overview of the colon cancer high-risk syndromes, with a focus on the availability and indications for genetic testing, is presented.