Hereditary pancreatitis is a rare autosomal dominant inherited disease with 80% penetration rate. The disease is characterized by recurrent episodes of pancreatitis often beginning in childhood, positive family history with at least two other affected members and no known precipitating factors. Most forms of hereditary pancreatitis are caused by one of two commoner mutations, R122H in exon 3 and N29I in exon 2 of the cationic trypsinogen (CT) (PRSS1) gene, located on chromosome 7. These genetic defects are speculated to cause excessive trypsin activity or to prevent inactivation of prematurely activated trypsin, resulting in pancreatitis. We performed mutation analysis of a Korean family with two members having clinically suspicious hereditary pancreatitis. We analyzed the CT gene in DNA samples extracted from peripheral blood of five family members. First of all, polymerase chain reaction and restriction enzyme digestion were performed in exon 3 of the CT gene. And then DNA products were purified and sequenced. We found out that three members of the family, the mother and two daughters, had a R122H mutation of the CT gene. We report the first family of hereditary pancreatitis associated with the CT gene mutation, an arginine to histidine amino acid substitution at residue 122, in Korea.