Objective To investigate the diagnosis and surgical management of adult choledochal cyst. Methods he clinical data of 58 adult patients with congenital choledochal cyst who were admitted to the First Affiliated Hospital of Nanjing Medical University from January 1997 to December 2010 were retrospectively analyzed. All patients were diangosed by the B ultrasonography, computed tomography (CT), Magnetic resonance cholangiopancreatography (MRCP) and endoscopic retrograde cholangiopancreatography (ERCP). Surgical procedures were selected according to the diagnosis and Todani classification. All data were analyzed using the t test or chi square test. Results The accurate rates of B sonography, CT, MRCP and ERCP were 78%(45/58), 92%(23/25), 9/9 and 5/5, respectively. Forty one patients underwent complete excision of the cyst+hepaticojejunostomy (2 patients were converted from laparotomy due to abdominal adhesions), 2 underwent resection of the cyst and involed hepatic segments+hepaticojejunostomy, 8 underwent laparoscopic excision of the cyst+hepaticojejunostomy, 1 underwent left hemihepatectomy, 3 underwent pancreaticoduodenectomy (including partial hepatectomy in 1 patient), 2 underwent common bile duct exploration+cholecystectomy due to acute obstructive suppurative cholangitis, 1 underwent external drainage of choledochal cyst due to advanced malignance. The mean operation time and postoperative duration of hospital stay of patients who received open and laparoscopic excision of the cyst and hepaticojejunostomy were (235±70)minutes, (320±50)minutes, and (10.0±2.3)days, (12.6±6.6)days, respectively, with significant differences between the 2 groups ( t=3.157, 2.162, P< 0.05). The postoperative morbidities of patients who received open and laparoscopic excision of the cyst and hepaticojejunostomy were 18%(7/39) and 3/8, respectively, with no significant difference (χ2=1.515, P >0.05). Canceration of the choledochal cyst was observed in 6 patients(10%). No perioperative mortality was observed, and the operative complication rate was 24%(14/58). The duration of the follow up ranged from 1 to 15 years, no severe long term complications were observed in patients with benign lesions. Four of the 6 patients with malignancy died in 1 year after operation, the other 2 patients survived for 3 years and 5 years, respectively.Conclusions Abdominal B ultrasonography should be the first choice for diagnosing adult congenital choledochal cyst, while MRCP is the gold standard. Surgical intervention should be timely considered once diagnosed. Complete excision of the cyst combined with Roux en Y hepaticojejunostomy is the first choice of treatment.