Introduction Hypophosphatemia often occurs during CRRT in adults. No pediatric study has been done on this problem. Objetive To analyze the efficiency and safety of the addition of sodium phosphate (P) to dialysate and replacement solutions. Methods Prospective study with intervention over two periods of time. Forty seven patients recieved CRRT with the standard solutions without P and 38 recieved CRRT with phosphate suplementation to dialysate and replacement solutions (0.8 ml/L). We define mild hypophosphatemia as: P 16 years, and severe hypophosphatemia: P 16 years. Results The incidence of hypophosphatemia with standard solutions (without P) was 85% and severe hypophosphatemia 57%. This incidence decreased in patients with phosphate suplementation to hypophosphatemia 55% (p The need for I.V. suplementation of P decreased from 36% to 10.5%. There were no clinic or analytic complications. The addition of phosphate to solutions does not precipitate with calcium in these concentrations. Conclusions The incidence of hypophosphatemia in children is very high. The addition of phosphate to dialysate and replacement solutions decreases the incidence of hypophosphatemia. This method is safe and reduces the necessity of I.V. P reposition.