The vesicouretral reflux is an important pathology that has an incidence of about 1% in children, and may be associated with renal scarring and hypertension due to kidney failure. The reason for this insufficient ureterovesical valve is based on congenital dysplasia, atrophy and architectural derangement of smooth muscle fibers of the distal ureteral muscle wall. The ureterovesical junction is a way of avoiding the reflux from the bladder to the higher urinary system (ureters and kidneys). This junction has a valve-like action. One important factor on the prevention of the reflux is the length of the intravesical ureter. These conditions (ureterovesical junction and length of the intravesical ureter) are, respectively, an active and a passive way of preventing reflux.