Choledochal cysts (CCs) are rare congenital cystic or fusiform dilatations of the biliarytree that can involve the extrahepatic and/or intrahepatic biliary tree. We report a case ofhuge type I CC associated with an aberrant posterior hepatic duct. A 52-year-old manpresented with a 3-week history of upper right abdominal pain and jaundice andserologic sign of obstructive jaundice. Ultrasonography (US), magnetic resonancecholangiopancreatography and endoscopic retrograde cholangiopancreatographywere performed with the diagnosis of CC type I according to the classification ofAlonso-Lej and Todani-Watanabe. The indication for surgical resection was posed. Thecyst was completely resected and the biliary tract was reconstructed with a doublehepatico-jejunostomy using the same Roux limb, since during the surgical dissection abefore unrecognized anatomical variation of the right biliary tree (aberrant posteriorhepatic duct at VI–VII segment) was identified. The diagnosis of CC is often difficult andUS and magnetic resonance cholangiopancreatography are necessary to definite biliarydilatation. Endoscopic retrograde cholangiopancreatography should be the mostdefinitive and reliable procedure for the diagnosis and treatment of bilio-pancreaticdisorders. Gold standard treatment is surgery (bilio-jejunostomy) and frozen-sectionhistology should be performed to rule out the presence of cancer. In conclusion, surgeryis the gold standard for the treatment of CC type I and does not depend on the age ofpatients, based on a substantial lifetime risk of developing cholangiocarcinoma.Preoperative study is mandatory to assess the biliary tree morphology and to researchany anatomical variation.