An anomalous arrangement of the pancreatobiliary ductal system is usually observed in patients with a congenital choledochal cyst and is represented by a long common channel distal to the pancreatobiliary junction. According to the angle of the pancreatobiliary junction, anomalous junctions can be classified into four groups: right angle, acute angle, complex union, and normal union (presented here in the order of their incidence). The right-angle type tends to have cystic dilatation of the choledochus, whereas the acute-angle type generally has cylindrical dilatation. However, the grade and length of the stenosis on the distal part of the choledochus tend to determine the type of choledochal cyst. Cystic dilatation is usually observed in patients with high-grade and long stenosis, whereas cylindrical dilatation is seen in those with low-grade and short stenosis. Patients with an acute angle junction seem to only suffer from abdominal pain, and those in the complex union group tend to have jaundice and an abdominal tumor. A high amylase level in the bile within the cyst is observed frequently. In patients with obstructive jaundice, however, the amylase level is usually not elevated, because pancreatic juice cannot enter the choledochus.