Background: The acute renal failure (ARF) incidence in pediatric cardiac surgery intensive care unit (ICU) ranges from 5 to 20% of patients. In particular, clinical features of neonatal ARF are mostly represented by fluid retention, anasarca and only slight creatinine increase; this is the reason why medical strategies to prevent and manage ARF have limited efficacy and early optimization of renal replacement therapy (RRT) plays a key role in the outcome of cardiopathic patients. Methods: Data on neonates admitted to our ICU were prospectively collected over a 6-month period and analysis of patients with ARF analyzed. Indications for RRT were oligoanuria (urine output less than 0.5 ml/kg/h for more than 4 h) and/or a need for additional ultrafiltration in edematous patients despite aggressive diuretic therapy. Results: Incidence of ARF and need for RRT were equivalent and occurred in 10% of admitted neonates. Eleven patients of 12 were treated by peritoneal dialysis (PD) as only RRT strategy. PD allowed ultrafiltration to range between 5 and 20 ml/h with a negative balance of up to 200 ml over 24 h. Creatinine clearance achieved by PD ranged from 2 to 10 ml/min/1.73m2. We reported a 16% mortality in RRT patients. Conclusion: PD is a safe and adequate strategy to support ARF in neonates with congenital heart disease. Fluid balance control is easily optimized by this therapy whereas solute control reaches acceptable levels.