This prospective, randomized, double-blind study was performed to compare the incidence of contrast-induced nephropathy (CIN) after the administration of the iso-osmolar contrast medium iodixanol to the low-osmolar contrast medium iopromide during coronary angiography in patients with impaired renal function. Patients with creatinine clearance (CrCl) <60 ml/min who underwent coronary angiography and/or percutaneous coronary intervention were randomized to receive either iodixanol (n = 215) or iopromide (n = 205). The primary study end point was the incidence of CIN, which was defined as an absolute increase in serum creatinine (SCr) ≥0.5 mg/dl (44.2 mol/L) or a relative increase ≥25% compared to baseline SCr. The secondary end points were the proportion of patients with increases in SCr ≥0.5 mg/dl, the proportion with SCr increases ≥1.0 mg/dl (88.4 mol/L), and the peak increase in SCr. Age, the presence of diabetes mellitus, mean baseline SCr, CrCl, the use of N-acetylcysteine, contrast volume, and the predicted risk score for CIN were similar in the 2 groups. CIN developed in 39 patients (9.3%); there was no significant difference between the iodixanol and iopromide groups (10.7% and 7.8%, respectively; absolute difference 2.9%, 95% confidence interval -3.1% to 8.9%, p = 0.394). The proportions of patients with SCr increases ≥0.5 mg/dl (6.5% vs 6.3%) and ≥1.0 mg/dl (2.8% vs 2.9%) were similar in the 2 groups. There was a tendency for more patients with relative increases ≥25% (10.2% vs 6.8%) and greater peak increases in SCr (0.037 ± 0.375 vs 0.029 ± 0.351 mg/dl) to be in the iodixanol group, but these differences were not statistically significant. In conclusion, the incidences of CIN after coronary angiography did not significantly differ between the iodixanol and iopromide groups in patients with impaired renal function.