ABSTRACT Purpose Emerging data demonstrate that injection of dextranomer/hyaluronic acid (Dx/HA) copolymer (Deflux, Q-Med Scandinavia, Uppsala, Sweden) is a safe and effective treatment for most patients with vesicoureteral reflux (VUR). We sought to determine the efficacy and factors predictive of outcome in patients treated with Dx/HA. Materials and Methods A total of 180 children 7 months to 15 years old (mean age 4.6 years) underwent subureteral injection of Dx/HA for VUR between October 2001 and February 2003. Dx/HA was injected submucosally within or beneath the intramural ureter. The average volume of injected material was measured for each ureter. At 2 weeks and 3 months postoperatively bladder ultrasounds were performed to measure the volume of Dx/HA (mm 3) in the trigone using the volume of an ellipsoid (V = 4/3πr 1r 2r 3). Renal sonography was performed to determine whether hydronephrosis was present. At 3 months fluoroscopic voiding cystourethrograms were used to evaluate for the presence of VUR. Results A total of 292 ureters in 180 children were treated (112 bilateral cases). There were 141 girls and 39 boys. Mean maximum grade per patient was 2.6 (out of 5). Average injected volume per ureter was 0.83 ± 0.03 ml (830 ± 30 mm 3). At 2 weeks the average measured volume was 663 ± 70 mm 3 (18% decrease from original volume), which decreased an additional 1% by 3 months to 656 ± 103 mm 3. There were no cases of hydronephrosis at up to 12 months postoperatively. There were 134 patients with at least 3 months of followup. After 1 treatment 72% (96) were cured (grade 0), while 55% of the failures (21 of 38) were improved. New contralateral VUR was seen in 6 patients (4.5%) who had neither a history of VUR nor an abnormal appearing ureteral orifice at cystoscopy. A lower success rate (60%) was seen in the first 20 patients compared with the last 20 patients (80%). The cure rate per grade was 90% for grade I, 82% for grade II, 73% for grade III and 65% for grade IV reflux. Local migration of material caudal to the ureteral orifice was seen in 61% of patients (11 of 18) at the time of reinjection of Dx/HA after initial treatment failure. There was no statistically significant difference in age, grade, volume injected, bilaterality or gender when successes were compared with failures. Conclusions The majority of patients (72%) undergoing minimally invasive treatment of VUR with Dx/HA are cured after 1 treatment. Contralateral treatment of nonrefluxing ureters should be considered in view of the increased incidence of new reflux (4.5%) and absence of morbidity with Dx/HA injection. There is a definite learning curve with injection therapy. The location of injected material and experience with the technique appear to correlate with the outcome of the procedure.