Background: Although placement of a metallic stent is an established therapeutic option for the palliation of patients with malignant biliary obstruction, it remains unclear which stricture-related or stent-related factors influence stent patency. Methods: Metallic stents were inserted endoscopically in 68 patients (38 men, 30 women; mean age 70.2 ± 8.5 years) with malignant biliary obstruction. Patency rates were prospectively analyzed according to malignant stricture characteristics, including length, morphologic type, and degree of narrowing. Furthermore, patient age, initial serum bilirubin level, length of stent, time to adequate expansion, and the location of the distal end of the stent were evaluated as possible factors affecting the stent patency. Stent patency was assessed by using the survival analysis of the Kaplan-Meier estimation and Cox regression analysis. Results: Median overall stent patency was 231 days (range 27-379 days) and the overall rate of stent occlusion 41.2% (28/68). The causes of occlusion were tumor ingrowth in 23 patients (33.8%), distal overgrowth in 3 (4.4%), proximal overgrowth in 1 (1.5%), and encrustation with sludge in 1 patient (1.5%). No significant differences in patency rates according to patient age, initial serum bilirubin level, primary tumor type, length and morphologic type of stricture, and length and location of the distal end of the stent were found. Cox regression analysis demonstrated that the degree of narrowing assessed by cannula or guidewire passage and the time to adequate expansion of the stent were independent factors associated with stent patency. Conclusion: Early expansion of the stent and easy passage of larger-caliber instruments through the stricture were favorable factors for long-term patency of the Wallstent. (Gastrointest Endosc 2002;55:359-65.)