The development of new-generation flexible ureteroscopes has improved diagnostic and therapeutic endourological procedures. Despite technical improvement irrigation flow and quality of vision is often unsatisfactory. This study describes inter-manufactural differences in the latest available flexible ureteroscopes in terms of irrigation flow in correlation to different deflection angles and the use of 1.9 Fr. stone baskets. Irrigation flow measurements were performed in five new-generation flexible ureterorenoscopes with 3.6 Fr. working channels: Wolf (Uretero-Renoscope 270°), Storz (Flex-X² and Flex-X(c)), ACMI (DUR-D) and Olympus (URF Type P5) in 0°, 90° and 180° deflection. All measurements were carried out five times with an empty working channel as well as with inserted 1.9 Fr. stone baskets. Mean flow rates with empty instruments (SD) counted 50 ml/min (0.8), 50 (1.0), 48 (1.7), 48 (1.6) and 44 (0.7) for ACMI, Wolf, Storz (FlexX² and Flex-X(c)), and Olympus, respectively. Stone baskets significantly reduced irrigation flows in all tested ureteroscopes (p < 0.05). In channels with inserted baskets, the highest flow rates were measured for ACMI and Wolf with 12 ml/min (0.7) each. The lowest reduction of flow rate was detected in the ACMI and the Wolf ureteroscope (76.0%, 38 ml/min each). Measurements after flexion showed no significant differences between the ureteroscopes. Latest generation of flexible ureteroscopes offer various new product developments, including excellent deflection capacities. This study showed inter-manufactural differences in terms of irrigation flow rates with either empty or occupied working channels resulting in significant alterations in endoscopic view.