Ureteroscopy has become the diagnostic and therapeutic procedure of choice for many conditions of the upper urinary tract. Technology is progressing rapidly in endourology, facilitating both goals. As reported previously, we developed a 2F video image flexible ureteronephroscope. This instrument is the smallest caliber of all ureteronephroscopes available to date. Because of the small diameter the device can be inserted into the ureter cystoscopically in a manner similar to catheter insertion. The procedure is done with the patient under local anesthesia. We performed ureteronephroscopic procedures on 79 patients using mainly a 6F passively deflecting flexible ureteronephroscope, which consists of the aforementioned 2F video image flexible ureteronephroscope and a 3F working channel. The area to be viewed was accessed successfully in 41 of 43 patients (95%). Over-all, diagnostic maneuvers were successful in 64 of 79 patients (87%). We suggest that the 2F and 6F flexible ureteronephroscopes would be indicated when conclusive diagnosis for upper urinary disease is not obtained by other means.