Background Some studies have shown that antioxidant ascorbic acid has renal protective effects, but the beneficial effects of contrast-induced nephropathy prevention remain to be clearly shown. Therefore, we aimed to determine whether ascorbic acid pretreatment reduces the risk of contrast-induced nephropathy in a high-risk population of patients with renal insufficiency undergoing coronary angiography. Methods We conducted a prospective, randomized, controlled trial, involving 156 consecutive patients with chronic renal insufficiency (calculated estimated glomerular filtration rate<60 mL/min/1.73 m(2) and/or serum creatinine >= 1.1 mg/dL) undergoing coronary angiography. Patients were randomized to ascorbic acid (n=74, 3 g intravenous injection before the procedure and oral 1 g per day for 2 days after the procedure, ascorbic acid group) or sodium chloride alone (n=82, control group). All patients received pre-and postprocedure hydration. Results There was no difference between the ascorbic acid group and control group in mean peak increase in serum creatinine measured within 48 hours after coronary angiography, the primary study end point (0.012 +/- 0.146 vs 0.022 +/- 0.212 mg/dL respectively, p=0.216). The incidence of contrast-induced nephropathy, a secondary end point defined as increase of either >= 25% or >= 0.5 mg/dL in serum creatinine, was 5.4% in ascorbic acid-treated patients (4/74) and 6.3% in control group patients (6/82), a nonsignificant difference (p=0.690). There were also no differences between the 2 groups in the inhospital clinical outcomes or length of hospital stay. Conclusion Ascorbic acid pretreatment for short-term at high dose do not prevent renal function deterioration after administration of contrast medium in patients with baseline renal insufficiency undergoing coronary angiography.