AIM:To compare the clinical outcomes between 0.025-inch and 0.035-inch guide wires(GWs) when used in wire-guided cannulation(WGC).METHODS:A single center,randomized study was conducted between April 2011 and March 2013. This study was approved by the Medical Ethics Committee at our hospital. Informed,written consent was obtained from each patient prior to study enrollment. Three hundred and twenty-two patients with a na?ve papilla of Vater who underwent endoscopic retrograde cholangiopancreatography(ERCP) for the purpose of selective bile duct cannulation with WGC were enrolled in this study. Fifty-three patients were excluded based on the exclusion criteria,and 269 patients were randomly allocated to two groups by a computer and analyzed:the 0.025-inch GW group(n = 109) and the 0.035-inch GW group(n = 160). The primary endpoint was the success rate of selective bile duct cannulation with WGC. Secondary endpoints were the success rates of the pancreatic GW technique and precutting,selective bile duct cannulation time,ERCP procedure time,the rate of pancreatic duct stent placement,the final success rate of selective bile duct cannulation,andthe incidence of post-ERCP pancreatitis(PEP).RESULTS:The primary success rates of selective bile duct cannulation with WGC were 80.7%(88/109) and 86.3%(138/160) for the 0.025-inch and the 0.035-inch groups,respectively(P = 0.226). There were no statistically significant differences in the success rates of selective bile duct cannulation using the pancreatic duct GW technique(46.7% vs 52.4% for the 0.025-inch and 0.035-inch groups,respectively; P = 0.884) or in the success rates of selective bile duct cannulation using precutting(66.7% vs 63.6% for the 0.025-inch and 0.035-inch groups,respectively; P = 0.893). The final success rates for selective bile duct cannulation using these procedures were 92.7%(101/109) and 97.5%(156/160) for the 0.025-inch and 0.035-inch groups,respectively(P = 0.113). There were no significant differences in selective bile duct cannulation time(median ± interquartile range:3.7 ± 13.9 min vs 4.0 ± 11.2 min for the 0.025-inch and 0.035-inch groups,respectively; P = 0.851),ERCP procedure time(median ± interquartile range:32 ± 29 min vs 30 ± 25 min for the 0.025-inch and 0.035-inch groups,respectively; P = 0.184) or in the rate of pancreatic duct stent placement(14.7% vs 15.6% for the 0.025-inch and 0.035-inch groups,respectively; P = 0.832). The incidence of PEP was 2.8%(3/109) and 2.5%(4/160) for the 0.025-inch and 0.035-inch groups,respectively(P = 0.793).CONCLUSION:The thickness of the GW for WGC does not appear to affect either the success rate of selective bile duct cannulation or the incidence of PEP. AIM: To compare the clinical outcomes between 0.025-inch and 0.035-inch guide wires (GWs) when used in wire-guided cannulation (WGC). METHODS: A single center, randomized study was conducted between April 2011 and March 2013. This study was approved by the Medical Ethics Committee at our hospital. Informed, written consent was obtained from each patient prior to study enrollment. Three hundred and twenty-two patients with a na? ve papilla of Vater who underwent endoscopic retrograde cholangiopancreatography (ERCP) for the purpose of selective bile duct cannulation with WGC were enrolled in this study. Fifty-three patients were excluded based on the exclusion criteria, and 269 patients were randomly allocated to two groups by a computer and analyzed: the 0.025-inch GW group (n = 109) and the 0.035-inch GW group (n = 160). The primary endpoint was the success rate of selective bile duct cannulation with WGC. Secondary endpoints were the success rates of the pancreatic GW technique and precutting, sele ctive bile duct cannulation time, ERCP procedure time, the rate of pancreatic duct stent placement, the final success rate of selective bile duct cannulation, and the incidence of post-ERCP pancreatitis (PEP) .RESULTS: The primary success rates of selective bile duct cannulation with WGC were 80.7% (88/109) and 86.3% (138/160) for the 0.025-inch and the 0.035-inch groups, respectively (P = 0.226). There were no significant significant differences in the success rates of selective bile duct cannulation using the pancreatic duct GW technique (46.7% vs 52.4% for the 0.025-inch and 0.035-inch groups, respectively; P = 0.884) or in the success rates of selective bile duct cannulation using precutting (66.7% vs 63.6% for the final success rates for selective bile duct cannulation were 92.7% (101/109) and 97.5% (156/160) for the 0.025-inch and 0.035-inch groups, respectively (P = 0.113). There were no significant differencesin selective bile duct cannulation time (median ± interquartile range: 3.7 ± 13.9 min vs. 4.0 ± 11.2 min for the 0.025-inch and 0.035-inch groups, respectively; P = 0.851) 29 min vs. 30 ± 25 min for the 0.025-inch and 0.035-inch groups, respectively; P = 0.184) or in the rate of pancreatic duct stent placement (14.7% vs 15.6% for the 0.025- inch and 0.035- inch groups, respectively; respectively; P = 0.832). The incidence of PEP was 2.8% (3/109) and 2.5% (4/160) for the 0.025-inch and 0.035-inch groups, respectively the GW for WGC does not appear to affect either the success rate of selective bile duct cannulation or the incidence of PEP.