The role of acetylcysteine in the prevention of contrast-media-induced nephrotoxicity was retrospectively studied. The medical records of patients undergoing cardiac catheterization between January 2000 and March 2002 were reviewed. The outcomes of patients with serum creatinine (SCr) concentrations above 1.2 mg/dL who were undergoing cardiac catheterization with contrast agents and received prophylactic acetylcysteine with i.v. hydration were compared with those of a control group who did not receive acetylcysteine. SCr concentrations were recorded 24 hours before administration of the contrast agent and 48-72 hours afterward for both groups. Sixty patients were included in the study: 32 in the acetylcysteine group and 28 in the control group. Both groups were comparable in demographics, disease states, drug regimens, and risk factors for developing contrast-agent-induced nephrotoxicity. In the acetylcysteine group, the median SCr concentration before receiving the contrast agent was 1.7 mg/dL and remained the same afterward. The median SCr concentration in the control group before administration of the contrast agent and 48-72 hours afterward was 1.6 and 1.9 mg/dL, respectively. The median change in SCr concentrations was greater in the control group than in the acetylcysteine group (0.25 and 0 mg/dL, respectively) (p = 0.001). The percentage of patients developing acute renal failure was greater in the control group than in the treatment group (25% versus 12.5%, respectively) (p = 0.21). The use of prophylactic oral acetylcysteine, combined with i.v. hydration, significantly reduced SCr levels after the administration of contrast media.