Choledochal cyst (CDC) perforation with bile peritonitis is potentially fatal. This study aims to establish the optimal timing for a CDC operation. Data of 133 children with perforated CDCs managed at our institution between August 2011 and July 2017 were reviewed. The perforations were categorized: Type 1: Complete cyst perforation with ascites and general peritonitis (n=52), Type 2: Sealed perforation with a small amount of bile contained in a pseudocyst (n=37), and Type 3: Intra-mural perforation (n=44). The incidence of perforation decreased with age, being the highest during early infancy (42.1%). The mean γ-glutamyl transpeptadase (GGT) of Type 3 patients was significantly higher than the other two types and can be used as an independent predictive factor for trans-mural perforation (p=0.019, an area under the ROC curve of 0.725, the cut-off value: 614.9 U/L). Type 1 perforations are likely (44.2%) to occur at the junction of cystic duct and CDC with copious ascites whereas Type 2 (73%) and Type 3 (95.5%) perforations tend to occur at the distal intra-pancreatic portion of the CDC. The orifice of the papilla of Vater was located distal to the descending duodenum in 93.2% of patients. Among these children, 82.1% in infants younger than 1 year old had liver fibrosis compared to 42.1% for the whole group. Conclusions: An elevated GGT level can predict an impending CDC trans-mural perforation. CDC perforation and liver cirrhosis are more likely to occur in young infants. Therefore, an early surgery of CDC before perforation is advocated. This article is protected by copyright. All rights reserved.