Chronic pancreatitis (CP) is a continuing or relapsing inflammatory disease of the pancreas. Several studies have demonstrated that mutations in the cationic trypsinogen (PRSS1) gene and the cystic fibrosis transmembrane conductance regulator (CFTR) gene are causative of the pathogenesis in a subset of hereditary and/or idiopathic CP cases. Recently, the N34S alteration of the pancreatic secretory trypsin inhibitor (PSTI) gene has been suggested to be closely associated with the pathogenesis of hereditary and/or idiopathic CP. Herein we analyzed genetic alterations of the PSTI gene in 32 unrelated Japanese CP patients who developed juvenile-onset CP or had a family history of CP; 5 patients were found to harbor alterations in this gene. In 3 of these 5 patients, heterozygous N34S alterations were found; this frequency is significantly lower than that in Caucasian patients reported previously. Moreover, a novel homozygous G-to-A transition in the promoter region of PSTI at 215bp upstream from the translation initiation site (-215G>A) was observed in 2 patients. We further surveyed the -215G>A alteration in 117 normal individuals; none of these individuals harbored this alteration. Our results suggested that the -215G>A alteration, as well as the N34S alteration, is a predisposing factor for CP.