Ureteropelvic junction obstruction (UPJO) is a common, congenital urinary malformation in the pediatric age group. In most cases the diagnosis is made antenataly and resolves spontaneously. Postnatal diagnosis is made when symptoms of urinary tract infection or abdominal pain occur. We report a six-month-old girl with single kidney and known vesicoureteral reflux grade IV presenting with severe acute renal failure (ARF), requiring acute peritoneal dialysis (PD).After diagnosis of decompensated UPJO, a nephrostomy was performed, and renal function restored within seven days. UPJO was subsequently treated by open pyeloplasty. To our knowledge, this is the first case of UPJO requiring PD due to severe renal failure in a child. Children with UPJO and major morbidity of the contralateral kidney are at risk of renal failure and should therefore be followed carefully to prevent serious complications.