Aim: To clarify the factors affecting the success rate of endoscopic subureteral injection (ESI) treatment of vesicoureteral reflux (VUR). Method: All patients who had ESI treatment for VUR at our unit between 1999 and 2002 were retrospectively reviewed with regard to age, gender, causes of VUR, reflux grade, type of injected materials, number of injections, results of cystourethrograms (VCUG), and outcome. The injected implants were gluteraldehyde cross-linked bovine collagen (GclBC), dextranomers in sodium hyaluronan (DiSH) and calcium hydroxylapatite (CH). A successful result was defined as absence of VUR confirmed by VCUG performed 3 months after the ESI procedure. Basic descriptive statistics were performed along with the chi(2) test ( p < 0.05 was significant). Results: 50 children (81 ureters) consisting of 27 girls (43 ureters) and 23 boys (38 ureters) with a mean age of 7.4 +/- 4.6 years constituted the study group. Grade III VUR was the most prominent grade (42%, 34 ureters) noted in all age groups. There was no significant difference between boys and girls with regard to the number of each grade of VUR. The success rate of first ESI procedure was 55.6% and was similar in each grade of VUR varying from 50 to 66%. Repeated injections have resulted in an overall success rate of 84%. No significant difference was noted between the age groups with regard to the success rate of ESI. Repeated ESI procedures were found to be unsuccessful in grade V VUR when compared to other grades (p < 0.05). There was a significant difference between primary reflux (76.5%, 62 ureters) and exstrophic (21%, 17 ureters) patients with regard to the grade of VUR and success rate of ESI. Exstrophic patients presented with a higher incidence of grade V VUR (41%) and with a lower success rate of ESI (64.7%). DiSH was the most commonly used agent (47 ureters) followed by CH ( 22 ureters) and GclBC ( 12 ureters). The success rates of the ESI procedure by each material were 91.5, 81.8, and 58.3%, respectively. No significant difference was noted between DiSH and CH. Low success rates by GclBC were attributed to less usage of the material. 82% of the ESI procedures were done by surgeon A (49 ureters) and B (18 ureters) with a success rate of 96 and 72%, respectively. No significant difference was noted between A and B with regard to the success rate and type of injected material and the success rate in each grade of VUR (p > 0.05). No untoward effects were noted in short- and long-term follow-up (mean 4 8 +/- 1.2 years) of any patient. Conclusion: The ESI procedure provides a high success rate for the treatment of VUR which decreases in grade V VUR and presence of exstrophia vesica. Single injection of various materials has been found to be successful in most of the patients with grade II VUR, whereas grade IV and III patients have required repeated injections which have resulted in 100 and 94% success rates, respectively. Grade I VUR can be managed by (close follow-up and appropriate antibiotic therapy without any surgical and/or endoscopic intervention. Patients presenting with grade V VUR should undergo open surgery if the first trial of ESI procedure results in failure as repeated injections have proved to be unsuccessful in this grade. The success rate of the ESI procedure does not seem to be affected by the type of injected material and different surgeons performing the procedure after achieving the learning curve. Copyright (c) 2008 S. Karger AG, Basel.