Dietary protein restriction, progressive loss of renal adaptive capacity, and uremic toxicity may contribute to the development of malnutrition and water retention in severe chronic renal failure (CRF). Malnutrition is also common in children treated with chronic peritoneal dialysis (CPD). It is not clear how the start of CPD influences body composition of children with CRF. We used a bioimpedance analysis device (BIA 101S Akern) to measure resistance and reactance in 7 children, with residual creatinine clearance of about 5 mL/min/1.73 m2 at the start of CPD (t0) and repeated the test 6 months later (t1). Distance (D), which is considered a reliable index of hydration and nutrition, was obtained from resistance (R) and reactance (Xc) by calculating phase angle (PA). BIA values of our patients were compared with those of healthy children of the same statural age from a series of 551 controls. There was an overall improvement of Xc, PA, and D after 6 months of CPD. In some cases D did not normalize, which indicates that some children with CRF on a restricted protein diet may present changes of body composition that are only partially reversed by short-term CPD. The present indications for the start of CPD should probably be reassessed, at least in some cases, to prevent malnutrition.