ObjectiveTo evaluate the impact of the use of a ureteral access sheath during flexible ureterorenoscopy on stone-free rate in patients treated for upper urinary tract stones. Materials and methodsA descriptive study was conducted with an analytical variable correlation component. The population as defined in this study includes individuals with kidney or proximal ureteral stones, with an indication of flexible laser nephrolithotomy to manage stones in one surgical time. The population consisted of 60 patients, who were divided into two groups; those in which ureteral access sheath was used for the procedure (44 patients), and those in which it was not used secondary to access failure (16 patients). ResultsComparing the two techniques in terms of operation time, stone size, and stone-free rate, there were no significant differences observed. After performing exploratory multivariate analysis, the dimensions explained 94% of the variability of the model, and a correlation was found between the categories: non-use of ureteral access sheath with no occurrence of complications, operation time less than 90 minutes and stones with diameters less than 10 mm. ConclusionsFlexible laser nephrolithotomy with no ureteral access sheath is safe in patients with stones smaller than 10 mm, with no significant variations compared to the use of ureteral sheath. This means that it could be a surgical alternative for the treatment of upper urinary tract stones in patients in which ureteral access with an ureteral access sheath fails.© 2014 Sociedad Colombiana de Urología. Published by Elsevier España, S.L. All rights reserved.