PURPOSE: To report our experience with ureteral obstruction after injection of dextranomer/hyaluronic acid copolymer (Dx/Ha) to treat vesicoureteral reflux, and analyze its possible causes, management and outcome. MATERIALS AND METHODS: Retrospective review of patients undergoing injection of Dx/Ha. The charts of patients with clinically relevant ureteral obstruction were evaluated for indications, prior interventions, technique of injection and volume injected. Video recordings obtained during injection were analyzed to detect possible technical errors. RESULTS: Fifty-four patients (87 ureters) were treated with Dx/Ha injection in a 5-year period. Five ureters (5.7%) in five patients (9.3%) developed significant ureteral obstruction requiring intervention. Manifestations of obstruction included pain in two patients, urinary tract infections in one and loss of function in one. Increased serum creatinine was observed in a patient with a transplanted kidney. Four obstructions resolved spontaneously (two after percutaneous nephrostomy, two after placement of a ureteral stent) and one required reimplantation. Review of the videos did not reveal any deviation from the usual technique. The volumes injected in the obstructed cases (0.7-1.2ml) were in the usual range. CONCLUSIONS: In this series, the incidence of post Dx/Ha ureteral obstruction was higher than previously reported. Although 4/5 cases resolved spontaneously, they required drainage to relieve symptoms or to improve renal function. Surgeons need to be aware of this complication and include its possible occurrence in the informed consent obtained prior to injection.