Recent studies suggest a high prevalence of sphincter of Oddi dysfunction (SOD) in patients referred to specialized centers for sphincter of Oddi manometry (SOM). Whether these results can be generalized to other Centers is unknown. From September 1998 to April 2000, patients undergoing SOM were prospectively identified. Patients were classified as having either biliary or pancreatic SOD, according to the modified Milwaukee classification, and underwent SOM of either the biliary or pancreatic sphincter based on clinical history. SOD was diagnosed when the mean basal sphincter pressure was >40 mm Hg. Standard cholangiography and/or pancreatography were performed following manometry. Fifty-one patients were Studied (43 women, median age 46 years, range 7-74 years). Prior to SOM, patients were classified by the modified Milwaukee classification as biliary type I in 1 patient, type II in 8, and type III in 20; pancreatic type I in 4 patients, type II in 14, and type III in 3; and biliary type III and pancreatic type III in 1 Patient. Indications for SOM included abdominal pain in 35 patients (69%), recurrent idiopathic pancreatitis in 12 (24%), chronic pancreatitis in 3 (7%), and acute pancreatitis in 1 (2%). Overall, 30 patients (59%; 95% CI 41.1-76.9%) were found to have SOD; abnormal biliary sphincter pressure in 16 of 29 patients (55%) undergoing biliary manometry, and abnormal pancreatic sphincter pressures in 14 of 21 patients (67%) undergoing pancreatic sphincter manometry, and abnormal biliary and pancreatic sphincter pressures in 1. SOD was diagnosed in 1 biliary type I patient (100%), 4 type II patients (50%), and 11 type III patients (52.4%) with a mean pressures of 92, 47, and 80 mm Hg, respectively. SOD was identified in 4 pancreatic type I patients (100%), 7 type II patients (50%), and 3 type III patients (100%) with mean sphincter pressures of 83 mm Hg, 96 mm Hg, and 102 mm Hg, respectively. In conclusion, the prevalence of SOD in patients with suspected biliary disease was 55%, suspected pancreatic disease 66%, yielding an overall prevalence of SOD of 59%. These results confirm the high prevalence of SOD in patients referred for SOM.