Colorectal cancer (CRC) is one of the commonest cancers wordwide.The risk factors for CRC are both environmental and genetic.Approximately 75% of CRCs are sporadic; the rest are hereditary or belong to a familial syndromes.Identification of familial forms of CRC and their genes have enabled the development of several models of carcinogenesis.Molecular diagnostics tools are available on a routine basis for the commonest hereditary colon cancer syndromes e.g.: hereditary nonpolyposis colorectal cancer (HNPCC), familial adenomatosus polyposis (FAP), attenuated FAP (AFAP), MYH-associated polyposis (MAP)juvenile polyposis syndrome (JPS), Peutz-Jeghers syndrome (PJS) and also for some very rare syndromes as Gardner, Turcot, Muir-Torre and Cowden syndrome.However, these syndromes represent only a small fraction of the total number of cases, in the region of 5%.On the other hand, many of the molecular changes seen in familial forms of CRC are also involved in the development of sporadic cancers.Recent studies have shown that activating mutations in the K-RAS gene are associated in the sporadic form of CRC with a poor response to anti-EGFR therapies.The expert panel of the European Society of Pathology therefore recommended standard K-RAS mutation testing for all patients with stage Ⅱ to Ⅲ colorectal carcinomas.Accordingly, it is necessary to determine the K-RAS gene mutational status of colorectal cancer before making therapeutic decisions and it can be expected that a substantional number of patients would benefit from molecular diagnostics of the K-RAS gene.