Aims: Prophylactic oral N-acetylcysteine (NAC) has been widely used for prevention of contrast-induced nephropathy (CIN). However, clinical studies have not been demonstrating this effect consistently because of evidence that NAC can alter serum creatinine levels without affecting glomerular filtration rate (GFR). We investigated NAC for the prevention of CIN by monitoring creatinine and cystatin C. Methods: We enrolled 113 patients (49 patients in NAC group and 64 patients in control group) with normal to subnormal GFR who were scheduled for cardiovascular procedures. Patients in NAC group receive acetylcysteine 600 mg twice a day, on the day before and on the day of cardiovascular procedure. All patients received a periprocedural intravenous infusion ("volume expansion") of 1 ml/kg/h with 0.45% saline for 24 h (12 h before and 12 h after exposure to contrast medium). Serum cystatin C and creatinine levels were measured before and at 12, 24, and 48 h after procedure. Results: The incidence of cystatin C-based CIN was 28.5% (n = 14) in NAC and 23.4% (n = 15) in control group (p = 0.663) and serum creatinine-based CIN was 12.2% (n = 6) in NAC and 17.2% (n = 11) in control group (P= 0.468). In this study, oral NAC had no effect on the prevention of CIN in patients undergoing cardiovascular procedures. Conclusion: In this study, oral NAC administration does not reduce neither the incidence of cystatin C-based CIN nor serum creatinine-based CIN in patients undergoing cardiovascular procedures.