Background— The Mehran Risk Score (MRS) has been demonstrated to be clinically useful for prediction of contrast-induced nephropathy (CIN) after nonurgent percutaneous coronary intervention. We aim to validate the MRS in the setting of Primary percutaneous coronary intervention for prediction of both CIN and short- and long-term clinical outcomes. Methods and Results— We assigned 891 consecutive patients with ST-elevation–myocardial infarction undergoing primary percutaneous coronary intervention to 4 groups of risk of CIN (RC) according to MRS (low, medium, high, and very high risk). We evaluated CIN, death, and major cardiovascular and cerebrovascular events after 25 months' mean follow-up. At multivariable analysis, mortality in very high-risk group was more than 10-fold higher (hazard ratio [HR], 10.11; 95% confidence interval [CI], 4.83 to 21.1; P <0.001) when compared with the low-risk group and was also increased in the high-risk group (HR, 6.31; 95% CI, 3.28 to 12.14; P <0.001) and medium-risk group (HR, 3.18; 95% CI, 1.83 to 5.51; P <0.001). Similarly, an increasing effect was seen across MRS strata for major cardiovascular and cerebrovascular events both in the very high-risk group (HR, 3.79; 95% CI, 2.27 to 6.6.32; P <0.001), high-risk group (HR, 1.90; 95% CI, 1.31 to 2.75; P =0.001), and medium-risk group (HR, 1.42; 95% CI, 1.10 to 1.85; P =0.007). In addition, the HR for rehospitalization increased with the increasing RC groups (HR, 3.32; 95%CI, 1.96 to 5.63; P <0.001; HR, 3.11; 95% CI, 1.35 to 7.20; P =0.008; HR, 7.73; 95% CI, 2.97 to 20.10; P <0.001, respectively). The odds ratio for CIN was 2.84 (95% CI, 1.16 to 6.92; P =0.021) in the very high RC group, 1.33 (95% CI, 0.68 to 2.61; P =0.398) in the high RC group, and 1.10 (95% CI, 0.67 to 1.79; P =0.699) in the medium RC group, as compared with the lower one. Conclusions— The MRS may be applied in the primary angioplasty setting population and is able to predict CIN and to stratify patients for poor clinical outcomes both in the short- and long-term follow-up.