While cystic malformations of the main biliary tract are wellknown and classified, it is exceptional to find cystic malformations of the accessory biliary tract (cystic duct). An adolescent aged 15 years and an adult of 49 years were operated for cysts of the cystic duct revealed by associated lesions, a cyst of the common bile-duct and gallbladder stones respectively. Ultrasonography showed cystic lesions which opacification during intravenous cholangiography and endoscopic retrograde cholangiography (EPRC) proved to be related to the cystic duct. The radiography outline of the biliary pathways so obtained served as a guide to the operative procedure, consisting of excision of the accessory biliary tract in both cases combined with resection of the common bile-duct cyst in one case. The radiologic, anatomic and histologic findings distinguished the lesions encountered from other malformations of the accessory biliary tract and confirmed their derivation from the cystic duct.