A review of ultrasonographic urotract controls was done in 487 children (390 female and 97 male) in whom subureteral Teflon paste had been endoscopically infected in order to avoid vesicoureteral reflux. Dilatation of the upper urinary tract was visualized in 91 of 732 ureters (12.43%). Upper urotract dilatation may be either a sign of the obstruction of ureterovesical junction caused by Teflon or recurrence of vesicoureteral reflux. Echosonographically, 4 types of dilatation were disclosed, each having, a particular diagnostic or therapeutic approach. Acute dilatations associated with pain (2 patients-0.4%) were subjected to emergency surgery (ureterocystoneostomy). Chronic dilatation, which did not abate even after 4 weeks (6 ureters-0.81%) was identically treated. A temporary dilatation usually withdrew spontaneously after 1-2 weeks (66 ureters-9.01%). Patients with delayed occurrence of intermittent dilatation (17 ureters-2.32%) underwent control micturating cystosonography for suspected reflux recurrence.