Forme fruste choledochal cyst (FFCC) is one of the diverse types of choledochal cyst with little or no dilatation of the extrahepatic bile duct (EHBD). It is considered that FFCC has to do with the pancreatobiliary malunion (PBM). In children, 3 to 6 millimeters of EHBD is assumed to be normal. Even though there is no clear-cut definition, FFCC is likely to be associated with bile duct dilatation less than 10 millimeters. Almost all cases have PBMs and symptoms of the pancreatitis or cholangitis. We experienced a case of FFCC in a 4-year-old boy. His EHBD measures 10 mm diameter. He had symptoms of pancreatitis and elevated hepatic transaminases. The pancreatobiliary common channel was 28 millimeters. He underwent EHBD resection and Roux-en-Y hepaticojejunostomy and was discharged with no specific complications.