Purpose: While the use of ureteral access sheaths facilitates flexible ureteroscopy, buckling or kinking of the device may preclude its successful application. We evaluate the ability of 2 hydrophilic coated ureteral access sheaths to obtain and maintain access to the upper collecting system. Materials and Methods: A total of 54 flexible ureteroscopy procedures were randomized to use of the 12/15Fr Applied Access Forte XE (Applied Medical, Rancho Santa Margarita, California) or the 12/14Fr Cook Flexor (Cook Urological, Spencer, Indiana) access sheaths. Device failure was defined as buckling of the sheath that prevented adequate placement, kinking of the sheath after removal of the obturator or difficulty in passing instruments through the sheath. The ease of placement, instrument passage and stone extraction was scored from poor (1) to excellent (4). Fisher's exact test and Mann-Whitney tests were used for statistical comparisons. Results: No patient required ureteral balloon dilation. There was no significant difference between the groups in regard to preoperative stenting (34% and 31%, p = 1.00) or rigid ureteroscopy before sheath placement (32% and 25%, p = 0.751). The device failure rate was 44% for the Applied sheath and 0% for the Cook sheath (p <0.001). Failures with the Applied sheath included buckling (25%), kinking (25%) and difficulty passing instruments (13%). The Cook sheath was rated superior with regard to ease of placement (3.89 vs 3.00, p = 0.001), ease of instrument passage (3.97 vs 3.29, p = 0.001) and ease of stone extraction (3.74 vs 3.00, p = 0.023). Conclusions: The performance of the Cook Flexor sheath was superior with regard to overall failure and ease of use.