Editor—Hereditary non-polyposis colorectal cancer (HNPCC) syndrome is a common autosomal dominant predisposition to colorectal cancer. Clinical diagnostic features of sporadic and HNPCC associated colorectal cancer do not differ significantly and until recently the identification of HNPCC patients was based mainly on their family history. Because of the importance for relatives of HNPCC patients to be clinically examined frequently in order to detect the disease at an early, curable stage, the International Collaborative Group (ICG) on HNPCC proposed criteria for identification of HNPCC families. According to the guidelines agreed by the ICG in Amsterdam in 1990, an HNPCC family has to fulfil the following criteria: there should be at least three relatives with colorectal cancer (one of whom is a first degree relative to the other two), at least two successive generations should be affected, and one relative should be diagnosed under the age of 50.1 CRC patients with HNPCC syndrome can also develop cancer of the endometrium, stomach, ovary, and urinary and hepatobiliary tracts.2-5 In several epidemiological studies, the incidence of HNPCC has been estimated to be between 0.5%6 and 15%3 of all colorectal cancers. The identification of mismatch repair genes (MMR), of which at least five (hMLH1,7 8 hMSH2,9 10 PMS1,9 10 PMS2,7 and hMSH6(GTBP)11) are associated with HNPCC, has enabled mutational analysis in families fulfilling complete or partial Amsterdam criteria. Carriers of germline MMR mutations have a higher than 80% risk for cancer by the age of 75.2 The great majority of germline mutations were found in approximately equal proportions in hMLH1and hMSH2, while mutations in the other three MMR genes have been reported only in a limited number of cases.12 Germline hMLH1 andhMSH2 mutations were …