The purpose of this study was to elucidate the function of the sphincter of Oddi (SO) in patients with juxtapapillary duodenal diverticula (JDDs). The SO function was evaluated by intraoperative biliary manometry in three groups of patients. Group 1 consisted of nine patients with JDDs and a dilated common bile duct (CBD) (diameter > 10 mm). Group 2 consisted of six patients with JDDs and a normal-sized CBD (diameter < 10 mm). Group 3 consisted of 26 patients without JDDs and with normal-sized CBDs. In the absence of a duodenal pressure load, the patients in group 1 demonstrated a lower baseline SO pressure and lower resistance of the biliary outflow than patients in group 3. They also demonstrated a lower baseline SO pressure and shorter decay time (which represented terminal biliary ductal resistance) than patients in group 2. In the presence of a duodenal pressure load of 300 mm H2O, the patients in group 1 demonstrated a lower incidence of phasic SO contractions, a higher baseline SO pressure, and a higher resistance of the biliary outflow than group 2 and group 3 patients. The decay time in group 1 and group 2 patients was higher than that of group 3 patients. Based on these findings, we conclude that the SO function in patients with JDDs is impaired owing in part to long-standing compression of the terminal biliary ductal system by a distended JDD associated with a rise in intraduodenal pressure in daily life.