A 31 year old man was hospitalised with general fatigue and epigastric pain. Abdominal ultrasonography, computed tomography, and magnetic resonance imaging showed a cystic lesion in the left lobe of the liver. Endoscopic retrograde cholangio-pancreatography and percutaneous trans-hepatic cholangiography revealed a localised dilatation of the intrahepatic bile duct without any obstruction. However, a large mass of mucinous material was noted in the saccular intrahepatic duct and the common bile duct. There was no evidence of a choledochal cyst, anomalous pancreaticobiliary ductal union, or congenital cystic change of the kidneys. A possible diagnosis of mucinous cystic neoplasm of the intrahepatic bile duct was made and a left hepatectomy performed. Cholangiography of the resected specimen showed a non-obstructive solitary cystic dilatation of the left hepatic duct. Histologically, the dilated duct was lined with columnar biliary epithelium without any papillary proliferation and/or atypia. Neither malignancy nor hepatic fibrosis was observed; the term "solitary cystic dilatation of the intrahepatic bile duct" perhaps is more descriptive and the concept easier to understand.