Objectives. To determine the differential effects on renal pressures and irrigation flow associated with the application of different ureteral catheters during percutaneous nephrolithotomy. Methods. Using ex vivo fresh cadaveric tissue, we established a percutaneous nephrolithotomy model. After obtaining lower pole percutaneous access, we recorded the pressure and irrigant flow measurements. Measurements were made with an empty ureter, 6F ureteral catheter, occlusion balloon catheter, and ureteral access sheaths (10/12F and 12/14F). Three 1-minute trials for each condition were recorded in each of four kidneys. Results. Ureteral catheterization with both the 10/12F and the 12/14F ureteral access sheaths resulted in significantly decreased intrarenal pressures in the pressure range tested compared with an empty ureter, a ureteral catheter, or an occlusion balloon application. Total irrigant flow for the 12/14F ureteral access sheath was significantly higher than for the empty ureter, ureteral catheter, or occlusion balloon in the entire pressure range evaluated. Conclusions. In this in vitro cadaveric model, application of the ureteral access sheath during percutaneous nephrolithotomy resulted in decreased intrarenal pressures and increased irrigant flow.