We recently experienced a rare case of chronic pancreatitis in a 13-year-old Japanese boy. Recently, in hereditary pancreatitis patients, some mutations have been identified in the trypsinogen gene. The purpose of this study was to investigate whether the same mutations could also be found in this patient. Polymerase chain reaction (PCR)-amplified products of his cationic and anionic trypsinogen genes were examined by direct sequence analysis. The gene analysis failed to show any mutation in any exons and their flanking intronic sequences of his trypsinogen genes. These findings indicate that the chronic calcifying pancreatitis in the present patient is "idiopathic", and thus a rare case of juvenile pancreatitis.