Choledochal cysts (CCs) are rare congenital cystic or fusiform dilatations of the biliary tree that can involve the extrahepatic and/or intrahepatic biliary tree. We report a case of huge type I CC associated with an aberrant posterior hepatic duct. A 52-year-old man presented with a 3-week history of upper right abdominal pain and jaundice and serologic sign of obstructive jaundice. Ultrasonography (US), magnetic resonance cholangiopancreatography and endoscopic retrograde cholangiopancreatography were performed with the diagnosis of CC type I according to the classification of Alonso-Lej and Todani-Watanabe. The indication for surgical resection was posed. The cyst was completely resected and the biliary tract was reconstructed with a double hepatico-jejunostomy using the same Roux limb, since during the surgical dissection a before unrecognized anatomical variation of the right biliary tree (aberrant posterior hepatic duct at VI-VII segment) was identified. The diagnosis of CC is often difficult and US and magnetic resonance cholangiopancreatography are necessary to definite biliary dilatation. Endoscopic retrograde cholangiopancreatography should be the most definitive and reliable procedure for the diagnosis and treatment of bilio-pancreatic disorders. Gold standard treatment is surgery (bilio-jejunostomy) and frozen-section histology should be performed to rule out the presence of cancer. In conclusion, surgery is the gold standard for the treatment of CC type I and does not depend on the age of patients, based on a substantial lifetime risk of developing cholangiocarcinoma. Preoperative study is mandatory to assess the biliary tree morphology and to research any anatomical variation.