To investigate the factors affecting the patency of biliary stents, we performed univariate and multivariate analyses in 370 straight stents with diameters of 10- to 12-French gauge which had been inserted singly as palliative treatment in 228 patients with malignant biliary obstructive disease. In the analysis of 226 first stents, advanced age of patients and higher serum bilirubin levels before insertion were found to be significant unfavorable factors limiting the duration of stent function. Overall, older age, male sex, no stent cleaning, and insertion on three or more occasions were significant unfavorable prognostic factors for patency. The risk of occlusion for stents inserted on three or more occasions was 2.32 times that of the first stent insertion. The median duration of patency of first, second, and subsequent stents was 177, 98, and 97 days, respectively. Diagnosis and the area of stenosis were unrelated to patency. No predictive significance of length or size of stent between 10- and 12-French gauge was found in our study.