The cumulative incidence rate of metachronous colorectal cancer in patients younger than 40 years of age at diagnosis of the primary cancer has been shown to be 30 percent. Metachronous colorectal cancer is predominantly located in the right colon with a decreasing frequency toward the rectum. The risk of developing a metachronous colorectal cancer was found to be 16-29 times increased when compared with the risk of having a primary colorectal cancer. Because of the resemblance between characteristics of metachronous colorectal cancer and the features of hereditary nonpolyposis colorectal cancer (HNPCC), it is proposed that young colorectal cancer patients developing metachronous colorectal cancer could in fact be HNPCC patients.