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ABSTRACT Background and Aim: Hereditary non polyposis colorectal cancer (HNPCC) is an autosomal dominant syndrome. The cancer appears between 40 and 50 years of age. Mutation in mismatch repair genes can lead to this cancer .One of the genes which is involved in this disease is PMS2 gene. Here, we present a case with a novel germline mutation in PMS2 gene. The aim of this report was to examine PMS2 gene and identify novel germline mutations in this gene. Case presentation: A 77-year-old male with diagnosis of colorectal carcinoma was referred for genetic testing. He suffered from a polyp with a diameter of 6.8 cm in hepatic flexure. The patient did not meet Amsterdam Criteria and Bethesda Guidelines, but screening for HNPCC was performed on account of pathological findings. Blood sample was used for identification of mutation and the paraffin embedded block was prepared for MSI analysis. Conclusion: One mutation in PMS2 gene was detected by analysis of the amplicon sequencing. The mutation was a transitional mutation in position 676 which led to transformation of guanine to adenine resulting in substitution of glutamic acid for glycine. Immunohistochemistry confirmed abnormal expression of PMS2 gene and MSI assay showed instability of sequenced amplicons in this gene. Conflict of Interest: Nil Received: Mar 11, 2012 Accepted: Apr 7, 2013