The role of urethrocystoscopy in the evaluation of vesico-ureteral reflux is discussed. In addition to voiding cystourethrograms and excretory urography endoscopic examination of patients with vesico-ureteral reflux permits the determination of the extent of the uretero-vesical junction malformation. The length of the submucosal ureter, the orifice configuration and its location as well as the trigonal muscular development are parameters which lend themselves to endoscopic evaluation. Their importance in the decision of whether vesico-ureteral reflux is treated conservatively or surgically is discussed. In addition, urethrocystoscopy may give valuable information on the causes of secondary vesico-ureteral reflux.