AIM: To study the clinicopathological and molecular genetic characteristics of typical Chinese hereditary nonpolyposis cotorectal cancer (HNPCC) families.METHODS: Four typical Chinese HNPCC families were analyzed using microdissection, microsatellite instability analysis, immunostaining of hMSH2 and hMLH1 proteins and direct DNA sequencing of hMSH2 and hMLH1 genes.RESULTS: All five tumor tissues of 4 probands from the 4typical Chinese HNPCC families showed microsatellite instability at more than two loci (MSI-H or RER +phenotype). Three out of the 4 cases lost hMSH2 protein expression and the other case showed no hMLH1 protein expression. Three pathological germline mutations (2 in hMSH2 and 1 in hMLH1 ), which had not been reported previously, were identified. The same mutations were also found in otler affected members of two HNPCC families,respectively.CONCLUSION: Typical Chinese HNPCC families showed relatively frequent germline mutation of mismstch repair genes. High-level microsateliita instability and loss of expression of mismatch repair genes correlated closely with germline mutation of mismatch repair genes. Microsatellite instability analysis and immunostaining of miamstch repair gens might serve as effective screening methods before direct DNA sequencing. It is necessary to establish clinical criteria and molecular diagnostic strategies more suitable for Chinese HNPCC families.