OBJECTIVE: To evaluate the anatomy of the extrahepatic bile duct and to reveal its importance in the formation of acute calculous cholecystitis (ACC). STUDY DESIGN: Case-control study. PLACE AND DURATION OF STUDY: Department of General Surgery and Radiology, Kanuni Sultan Suleyman Training and Research Hospital of the University of Health Sciences, Turkey, between January 2016 and December 2021. METHODOLOGY: The data of the patients treated with ACC were analysed on MRCP by an experienced radiologist. The patients were divided into two groups; asymptomatic gallstones (AsGS, control group) and ACC. The cystic duct, common hepatic duct, and common bile duct lengths and variations in cystic duct opening were measured. Receiver operating characteristics (ROC) analysis was conducted to define a cut-off value and compared categorical results of the two groups by Mann-Whitney U test. RESULTS: One-hundred and seventy-three patients were analysed, one-hundred and seven were females, and 66 were males. The median age was 46 years in the AsGS group and 53 years in the ACC group. It was statistically significant that ACC had a higher median age value than AsGS (p=0.014). In the analysis of extrahepatic variations, cystic duct, common hepatic duct, and common bile duct length, were statistically longer in the calculous cholecystitis group (p<0.001, p=0.022, and p=0.019 respectively). ROC analysis was performed for cystic, common hepatic, and common bile duct length, respectively. Cut-off values ​​were 30.5 mm, 36.5 mm, and 42.5 mm. CONCLUSION: Extrahepatic bile duct variations are of critical importance in ACC surgery. In the data, as the cystic duct and common bile duct lengthens, the possibility of ACC increases. There is need for studies with larger samples. KEY WORDS: Acute calculous cholecystitis, Extrahepatic biliary tract, Anatomical variations, Cholelithiasis.