To determine the deterioration in the maximal active deflection and flow capabilities of a new-generation flexible ureteroscope (URS). We performed 50 ureterorenoscopies using the same URS: a Karl Storz 11278 AU1 Flex-X, which is capable of a 270 degree active deflection in the ventral and dorsal directions. Postoperatively, we evaluated the maximal active ventral and dorsal deflection, irrigation flow at 100 cm H2O, and the number of broken optical fibers. The URS was used for a total of 76 hours, 15 minutes (average 95 minutes per procedure). The maximal ventral deflection had deteriorated from 270 degrees to 208 degrees at the last procedure. The maximal dorsal deflection had decreased from 270 degrees to 133 degrees. The irrigation flow at 100 cm H2O had decreased from 50 mL/min initially to 40 mL/min at the last procedure. The number of broken image fibers had reached six at the 50th procedure. One repair was necessary at the 50th procedure because of a laser perforation of the working channel. The need for repair occurs less frequently with the new-generation of URSs, especially when they are used by an experienced endourologist. In the future, improvements in the durability of the flexible URS will still be key for widespread use of the technique and especially to limit damage by the laser to the working channel.