Objective: Replication errors (RER) is related to initiation and development of colorectal carcinoma (CRC).To investigate the different biological behavior of RER+ and RER- CRC. Methods: Silver staining PCR-single strand conformation polymorphism (PCR-SSCP) and denatured polyacrylamide gel electrophoresis methods were used to detect microsatellite instability (MSI) at 4 loci on chromosome 2, 5, 17 in paraffin-embedded specimens of 60 colorectal carcinoma (CRC) and their paired normal tissue.RER+ was scored if 2 or more loci behaved as gaining extra bands. Results: The results showed that RER+ was found in 19/60 CRC, among which 7 cases had a family history.According to the criteria of Amsterdam, 4 were diagnosed as hereditary nonpolyposis colorectal cancer (HNPCC), and of which 3 cases were RER+. The ratio RER+ in HNPCC (75%) was significantly higher than that among sporadic CRC (28.5%). Most of the RER+ CRC have the feature of poorly differentiated adenocarcinoma (P＜0.01), the tendency to involve the right side of the colon (P＜0.05), a higher proportion with a family history (P＜0.05), Duckes A and B stage (P＜0.05). Conclusion: The results indicated that RER+ is a relatively common molecular event in CRC.There are different clinico-pathological features and behavior between RER+ and RER- CPC.