We investigated a marked common bile duct wall contrast-enhancement in acute pancreatitis on CT scans as an accurate sign of biliary pancreatitis. Contrast-enhanced CT scans of 80 patients with clinically and biologically confirmed acute pancreatitis were reviewed by two gastrointestinal radiologists without knowledge of the cause of acute pancreatitis. Since this study was retrospective and then did not modify the CT examination routinely performed in acute abdomen, no institutional review board approval and informed consent was requested. A systematic measure of the difference between the CT number of common bile duct wall and the CT number of pancreatic parenchyma was performed. The "choledochal ring" sign, defined by a difference greater than 15 HU was specifically studied and compared to other factors often associated with biliary pancreatitis through univariate and multivariate analyses. Compared to other factors classically associated with acute biliary pancreatitis, the "choledochal ring" sign showed high specificity (100%) and high positive predictive value (100%). In patients with acute pancreatitis, the "choledochal ring" sign is a new and accurate finding of acute biliary pancreatitis on CT scans.