Endoscopic subureteral injection of bulking agents has become a widespread treatment for vesicoureteral reflux (VUR) in children. Various biological and plastic materials have been introduced for this purpose with different success and complication rates. Evaluations of this method in previous studies have focused on the success rate of eliminating VUR, whereas complications have been less frequently reported in detail. This report describes four children with VUR grade I to IV-V who experienced severe complications after endoscopic treatment with polydimethylsiloxane at the age of 5 months to 7 years. Three children developed urosepsis and two patients obstructive acute renal failure. These complications required repeated hospitalizations with extensive diagnostic and therapeutic procedures. Percutaneous nephrostomy was necessary in three patients and ureteroneocystostomy was eventually performed in all. These observations suggest that endoscopic treatment of VUR in childhood with polydimethylsiloxane can lead to severe postoperative complications and that a standardized follow-up should be an integral part of endoscopic procedures.