Introduction: The gallbladder and bile ducts originate through a complex process during the 4th gestational week; there is a wide variety in their anatomy., Objective: To identify the type, frequency, and association with certain pathologies of anatomic variations of bile ducts in patients in which endoscopic retrograde colangiography (ERC) was performed., Methods: Six hundred and six patients in whom ERCs were performed from 2005 to 2007 in the Endoscopio Unit at the Hospital General Dr. Manuel Gea González in Mexico City were included. Variations in bile duct anatomy seen in the X-ray taken during ERC were identified. Demographic characteristics of the patients, indications of the study, complications, treatments, and type of anatomic variant were registered. Descriptive statistics were used to analyze the information. X2 and Fisher´s exact test were also performed for the comparison between patients with and without anatomic variations., Results: We identified biliary anatomic variations in 5.1% of patients in the study. Among them, seventy- seven per cent were women, with a mean age of 41 years. The anatomic variation most frequently found was a low union of the cystic duct with the common hepatic duct. The main diagnosis during ERC was choledocholithiasis in 71% of patients. Bile duct injuries were found in only 3.2% of patients with anatomic variations., Conclusions: Anatomic variations in bile ducts identified by ERC are frequent in Mexican population; nevertheless they were not associated with the occurrence of bile duct injuries.