BACKGROUND : This study investigated the clinical outcomes of stent placement for malignant extrinsic ureteral obstruction (MUO) and predictive factors for stent failure. METHODS : We retrospectively analyzed clinical data for 91 patients with radiologically significant hydronephrosis due to MUO who underwent successful stent placement. In total, 132 ureters were stented for the decompression. Factors related to stent failure were analyzed with a Cox proportional hazards model. RESULTS : Stent failure occurred in 25 ureters in 20 patients. The median interval to failure was 63 days. The multivariate analysis showed that the significant predictors of stent failure were bladder invasion and severe hydronephrosis before the stent insertion. The patients were divided into three groups based on these two factors: low-risk (neither factor; 85 patients), intermediate-risk (one factor; 37), and high-risk (both factors; 10). The median stent failure-free survival rate at 3 months was 94.8% in the low-risk, 71.8% in the intermediate-risk and 55.6% in the high-risk group, respectively. Of the ureters with stent failure, there was successful re-replacement of internal stents in 3 low-risk, 6 intermediate-risk and no high-risk ureters. Replacement by nephrostomy was done in 2 low-risk, 5 intermediate-risk and 7 high-risk ureters. CONCLUSIONS : The patients considered at low-risk could be managed without stent failure by internal stenting. However, the patients at high-risk may require the consideration of nephrostomy or other alternatives as the initial treatment. Our stratification model may allow better risk stratification for patients with regard to ureteral stenting, helping to identify patients for whom ureteral stenting is indicated.