Endoscopic injection of Teflon paste under the submucosal portion of the ureter in the bladder is a new treatment for vesicoureteral reflux. Twenty-one children at The Montreal Children's Hospital and at St. Justine Hospital were treated with this technique over a 2-year period. In 15 children, abdominal sonography was performed 1-5 days after Teflon paste injections. Follow-up sonograms performed 5 weeks to 1 year after the procedure are available in nine children. Sonographically, the Teflon paste at the injection site appears as a hyperechoic focus within the bladder wall with distal shadowing seen postoperatively and on follow-up examinations. This finding occurred in 22 (88%) of 25 treated ureters. The location of Teflon paste after injection as viewed via cystoscopy is correlated with the sonographic appearance. This preliminary report suggests that sonography is useful in determining the location and size of the Teflon mass, in evaluating surrounding soft tissues at various time intervals after injection, and in assessing possible complications such as obstruction.