In this report, we describe the application of 3-dimensional (3D) sonography for diagnosing choledochal cysts in 3 girls who were 18 months, 2 years, and 11 years old. The 3D images that were obtained during the sonographic examination revealed that all 3 patients had a type I choledochal cyst and also demonstrated dilatation of the biliary tracts. The 3 patients then underwent surgical excision of their cysts, cholecystectomy, and hepaticojejunostomy. Besides its other clinical applications, 3D sonography promises to be a valuable adjunct to conventional 2-dimensional imaging for the evaluation of choledochal cysts in pediatric patients. (C) 2003 Wiley Periodicals, Inc.