Choledochal cyst was diagnosed before operation in 14 out of 16 infants and children by means of a combination of diagnostic tests. Ultrasonic echogram showed a cystic mass in all 11 patients examined. The characteristic displacement of the duodenum was noted in 9 of 14 patients by contrast studies of the upper gastrointestinal tract, and hepatobiliary scintiscanning confirmed choledochal cyst in 7 of 8 patients (88%). A cyst was shown by oral or intravenous cholangiography in 3 of 4 patients. Onset of symptoms occurred from 7 days of age to 9-5 years; in 10 patients onset occurred under 12 months of age, in 3 from 13 to 24 months, and in the remaining 3 from 2 to 9-5 years. The first symptoms were jaundice, vomiting, acholic stools, and poor sucking. Obstructive jaundice and acholic stools were found in more than 80% of the patients, and abdominal mass in 60%. Vomiting occurred in 50% of the patients, one-third of whom showed failure to thrive, and 70% of patients over the age of 1-5 years had abdominal pain. About half of the patients had a mild to moderate degree of fever. In all patients primary excision of the cyst was followed by hepaticojejunostomy in Roux-en-Y fashion. The postoperative course was uneventful in 14 patients; 2 patients died, one from ascending cholangitis and one from hepatic failure.