INTRODUCTION:: To determine the optimal time for routine exchange of indwelling percutaneous nephrostomies (PCNs) in patients with malignant urinary obstruction. METHODS:: Patients with urinary obstruction due to gynecologic malignancies who underwent placement of PCN that required at least one exchange from 2011-2013 were reviewed. Exchanges were classified as routine or due to one of three complication types: mechanical (tube dislodgement), obstruction, or infection. Charges for each complication type were defined as the median value from representative cases. The distribution of exchange types under different routine exchange frequencies was estimated with an Accelerated Failure Time Model and average yearly PCN-related hospital charges were estimated with a Markov Chain Monte Carlo model. RESULTS:: 33 patients with 57 exchange encounters were included. Median representative hospital charges were $3.4k for routine exchanges, $36.5k for infection, $10.5k for obstruction, and $8.3k for mechanical. The model predicted that with a 90-day routine exchange and 50% adherence, 25% of exchanges would be routine and 35% would be due to infection, which would improve to 47% and 20%, respectively, with a 60-day routine exchange and 75% adherence. Estimated yearly PCN-related hospital charges were $160.0k without mandated routine exchanges, and were lowest when routine exchange was performed at 60 days (savings of $22.9k ± $2.0k with 75% adherence). Projected savings increased as patient adherence improved, as projected savings with 60-day exchange were reduced to $7.6k ± $0.7k if adherence fell to 25%. CONCLUSION:: Scheduled routine PCN exchanges every 2 months is the least costly strategy for patients with malignant ureteral obstruction.