Hydroureteronephrosis (HUN) of the renal transplant (RT) can be obstructive or non-obstructive, refluxing or non-refluxing, and can cause allograft dysfunction. HUN of the RT as a manifestation of rejection is uncommon and has not been described in children. We describe two pediatric RT recipients who presented with late-onset HUN, 5 and 10 years after transplantation. Both had new-onset HUN which occurred at the time of rejection; HUN resolved in both patients after treatment of rejection. Renal function stabilized in both patients without the need for stent or nephrostomy tube placement. There was no obstruction or vesicoureteral reflux (VUR). Edema of the uroepithelial cells leading to transient obstruction causing HUN is a most likely explanation. We conclude that treatment of rejection in patients without obstruction or VUR may lead to resolution of HUN without the need for urological interventions.