Objectives To investigate the operation time (OT) and the ureteral access sheath (UAS) usage with the infection rates and to determine a cut-off value for OT Methods We retrospectively analyzed the data of the patients who underwent FURS for renal stones larger than 20 mm between 2010 and 2019. The investigated parameters were OT, UAS using, and infection status. The data were analyzed by forming two groups according to whether the OT was less than 60 minutes and more, whether the UAS was used and whether an infection occurred. In addition, independent risk factors that may affect postoperative urinary infection development were also investigated by logistic regression analysis. And, a ROC curve analysis was applied to determine a cut-off value in OT terms, where infection rates increase more. Results A total of 575 patients were enrolled in the study. The rates of the usage UAS and infection were greater statistically in the group for longer than 60 minutes. OT was longer statistically in the infection group than in the group without infection ( 94.1±14.2 and 68.01±23.1, for groups 1 and 2, respectively, p<0.05, Table 2). OT was statistically longer in the UAS group than unused one ( 79.3±24.4 and 66.7±22.4, for groups 1 and 2, respectively, p<0.05, Table 3). ROC analyses revealed a cut-off point of 87.5min for OT in terms of infection rate Conclusion While the infection risk increases when OT exceeds 60 minutes, FURS can be safely performed up to 87.5 minutes with 89% sensitivity and 69% specificity infection risk.