Background. There is little prospective data on whether bigger plastic stents are better for patients with malignant biliary obstruction with jaundice. Goals. Multicenter prospective study to compare technical success, clinical response, stent occlusion, and patient survival in patients with malignant biliary obstruction randomized to 10-French or 11.5-French plastic stent. Study. Patients with malignant biliary obstruction were randomized to 10-French or 11.5-French biliary stents. Patients were prospectively assessed for stent occlusion, stent-related interventions, hospital stay, and change in bilirubin. Main outcome measurements included technical success, clinical response, rates of stent occlusion, and survival. Results. 234 patients (47 hilar and 187 common bile duct strictures) were randomized. Outcomes were similar for the 10-French and 11.5-French groups (technical success 99.1% versus 97.4%, P = 0.37). Overall, median stent survival was 213 days, but there was no statistically significant difference in stent survival between 10-French and 11.5-French stents (149 versus 258 days, P = 0.16). Stent survival was significantly longer when placed for common bile duct versus hilar strictures (231 versus 115 days, P = 0.049). Conclusions. The theoretical advantage of improved bile flow for the 11.5-French stent does not translate into more prolonged patency, better clinical response, and longer patient survival than the 10-French stent.