INTRODUCTION:: Contrast-induced acute kidney injury (CI-AKI) may complicate the course of percutaneous coronary intervention (PCI) and may be associated with adverse outcomes. The aim of this study was to compare the effect of ionic versus nonionic contrast media (CM) on the development of CI-AKI in patients undergoing primary PCI and to determine risk factors for CI-AKI. METHODS:: This prospective observational cohort study included 102 patients with ST elevation myocardial infarction who were subjected to primary PCI. They either received the ionic CM ioxitalamate (53 patients) or the nonionic CM iohexol (49 patients). The incidence of CI-AKI was compared between the 2 groups as well as different demographic data, risk factors, and clinical and procedural data. Daily serum creatinine was recorded for all patients in the first 72 hours following the intervention and until discharge for patients who developed CI-AKI. CI-AKI was defined as a rise in serum creatinine by >0.3 mg/dL or by more than 1.5 times baseline, or urine volume <0.5 mL/kg/h for 6 hours in the 72-hour period following primary PCI. RESULTS:: Overall, CI-AKI occurred in 17 patients (16.7%). There was no significant difference in the incidence of CI-AKI between the ionic and the nonionic groups. Univariate regression showed that CI-AKI had significant correlation with older age (61.8 ± 8.0 years; P = .006), hypertension (P = .016), preexisting renal dysfunction (P = .025), hemodynamic instability (P = .03), complete revascularization (P = .031), and high contrast volumes exceeding the maximum allowed contrast dose (P = .027). After multivariable adjustment, old age and hypertension were still independent correlates of CI-AKI. CI-AKI was significantly associated with mortality (P < .001). DISCUSSION:: CI-AKI frequently complicates primary PCI and is associated with higher incidence of mortality. The incidence of CI- AKI seems to be comparable between ionic and nonionic CM post-primary PCI. Optimizing periprocedural hemodynamic stability and using the least possible volume of CM can minimize the risk of CI-AKI.