Three cases of choledochal cyst associated with intrahepatic biliary dilatation are presented. Findings on sonography included a large cystic mass in the porta hepatis separate from the gallbladder; a dilated common hepatic or common bile duct entering directly into the cyst; the smaller cystic masses of dilated central intrahepatic ducts. The dilatation of the central intrahepatic bile ducts was moderate in two patients and massive in one patient. All three patients underwent operation with intraoperative cholangiography. Two patients had 99mTc IDA cholescintigraphy which confirmed the diagnosis of choledochal cyst by demonstrating filling of the cyst with stasis and delayed intestinal activity. The accurate preoperative diagnosis of choledochal cyst, made by sonography combined with 99mTc IDA cholescintigraphy, obviated invasive studies.