Although institutional criteria vary, in general acute renal failure is defined when serum creatinine raises 25–50 % or 0.5–1 mg/dL. Serum creatinine peaks in 3–5 days but may be elevated as early as the first day. In young children creatinine levels may not be sensitive enough to detect renal failure; in these patients cystatin C levels or glomerular filtration values may be a more appropriate test. Risk factors for renal insufficiency induced by contrast are age >65 years, diabetes, end-stage liver disease, and severe congestive heart failure. Clinical manifestations are highly variable and may range from completely absence of urine to oliguria. Most effects are temporary and reversible. In mild cases, serum creatinine returns to normal in 2 weeks. When severe, dialysis may be necessary. The major preventive action against nephrotoxicity is to ensure adequate hydration. One possible protocol would be 0.9 % saline at 100 ml/h, beginning 6–12 h before and continuing 4–12 h after intravascular iodinated contrast medium administration. Pediatric infusion rates are variable and should be based on patient weight.