Objectives: Malignant ureteral obstruction (MUO) is a devastating complication of cancer, and it is commonly treated by drainage via percutaneous nephrostomy (PCN). The objective of this study was to determine the efficacy, safety, and functional outcome of tandem ureteral stents (TUS) in the management of MUO. Materials and Methods: The medical records of all patients with MUO who underwent balloon dilation and TUS insertion in Sheba Medical Center between 2014 and 2018 were retrospectively analyzed. Safety was measured by intra- and postoperative complications, efficacy by time to event analysis, and failure by the requirement of PCN attributable to renal failure or infection. Independent risk predictors of TUS failure were determined by a multivariable Cox regression analysis. Results: A total of 103 procedures were performed on 81 patients during the study period. The median follow-up was 32 weeks (interquartile range [IQR] 24-67). Fifty-nine (72.9%) patients remained with TUS while 22 patients required PCNs. The median time to procedural failure was 4 months (IQR 2-8). Complications developed after 18 (22.2%) procedures. Two patients requested stent removal due to lower urinary tract symptoms. Independent predictors for TUS failure were metastasis (hazard ratio [HR] 3.03, 95% confidence interval [CI] 1.27, 7.23, p = 0.013) and prior PCN (HR 3.38, 95% CI 1.40, 8.13, p = 0.007). Conclusions: TUS is an efficient and safe management option for patients with MUO. It can alleviate renal failure without the need for an external PCN. Metastasis and prior PCN are associated with TUS failure.