The present research was aimed at defining the surgical anatomy of the biliopancreatic ducts and of Oddi's sphincter. The numerous anatomic variations of the papilla, the millimetric distribution of its muscle fibres, and any morphological detail of clinical significance have been investigated. An integrated analysis of radiographic, tridimensional (casts), and histologic findings has been carried out in 49 of 64 autoptic bilio-duodenopancreatic specimens. Exact limits of the choledocus and Wirsung sphincters were defined. A consistent accumulation of circular muscle fibres could be seen, on the choledocus duct side, up to a mean distance of 13.6 mm from the papillary pore. However, more rarefied fibres were present up to 20.5 mm. Muscle fibres were seen to stop roughly on the pancreatic duct side at 7.3 mm from the papillary pore. The beginning of the sphincter was observed 2-3 mm above the papillary pore. There was no evidence suggesting the presence of upper, middle, and lower biliary sphincters. Five anatomic diversities of the Wirsung-choledocus confluence were found. The Y type was the most frequent (61.2%), followed by the U type (22.4%), V (14.3%), and II (2.1%). Santorini's duct with a normal papilla was present in 16 per cent of the cases. These data along with other interesting observations on antireflux mechanisms (Santorini's valves) and on the ductal space orientation appear to be useful guidelines for a physiopathological understanding of bilio-pancreatic diseases and for any therapeutic procedure on these structures.