Opie suggested in 1901 that a common channel between the pancreatic duct and the common bile duct is created when a gall stone becomes impacted at the duodenal papilla. He proposed that bile would regurgitate into the pancreas and trigger pancreatitis. The case is reported of a 22 year old woman with an impacted stone at the duodenal papilla creating a common channel. The patient suffered from acute pancreatitis. Three days before the onset of pancreatitis, however, a T drain had been inserted into the common bile duct from which bile had been flowing freely and continuously. Moreover, amylase activity in fluid from the T drain was 49,000 U/l at the onset of pancreatitis pointing to reflux of pancreatic juice into the biliary tract. The amylase activity in bile decreased rapidly after endoscopic papillotomy and retrieval of the stone. The events participating in the development of acute gall stone induced pancreatitis in this patient with a common channel situation permitted reflux of pancreatic juice into the biliary tract rather than bile into the pancreas. Impairment of pancreatic outflow by a gall stone was probably the primary triggering event, rather than the regurgitation of bile into the pancreas. Preventive or therapeutic treatment in gall stone pancreatitis should be aimed at the urgent restoration of pancreatic flow rather than at the prevention of a hypothetical bile reflux.