Since 1959 when Alonzo-Lej and colleagues introduced the modern era of treatment of choledochal cysts, much information has come to light, particularly from Japan where the incidence of choledochal cyst is much higher than in occidental countries. While the original classification of Alonzo-Lej is still in use, additional forms of the anomaly have been identified by modern imaging techniques. Antenatal ultrasound studies and accurate cholangiography have made it possible not only to better define these anomalies but also to provide information regarding etiology. It seems most likely that choledochal cysts are the result of pancreatic reflux into the biliary tree from an anomalous junction of the main pancreatic duct with the common bile duct. Ultrasound, radioscintigraphic studies, and various forms of cholangiography have made the diagnosis straightforward. Although many approaches to treatment have been tried over the years, the most successful approach is total cyst excision with Roux-en-Y hepaticojejunostomy. This provides excellent long-term results with minimal complications. Nonetheless, lifelong follow-up is necessary to avoid potential problems such as biliary cirrhosis. Other forms of choledochal cysts, such as choledochocele and Caroli's disease, are treated as the anatomy dictates and these individuals must be followed long term as well. The overall results are most gratifying.