Ureteral obstruction after transurethral injection therapy for primary vesicoureteral reflux is known to occur in less than 1% of cases. We report the first case of a ureteral obstruction after transurethral injection of dextranomer/hyaluronic acid copolymer (Deflux) for the treatment of secondary vesicoureteral reflux after renal transplantation. Loss of transplant function made reimplantation of the ureter necessary. A periureteral phlebitis and moderate foreign body reaction was found histologically, although the patient had received immunosuppressive therapy. Endoscopic therapy of secondary vesicoureteral reflux in patients after renal transplantation is a reasonable minimally invasive treatment option; however, severe complications may occur.