Objective: The systemic immune-inflammation index (SII), derived from counts of neutrophils, platelets, and lymphocytes, has been developed to predict clinical outcomes in several cancers and cardiovascular diseases. The aim of this study was to evaluate the utility of SII to predict contrast-induced nephropathy (CIN) in patients with ST-segment elevation myocardial infarction (STEMI) who underwent primary percutaneous coronary intervention (PCI). Methods: A total of 632 patients with STEMI who underwent primary PCI were retrospectively included. The patients were divided into two groups based on the presence or absence of CIN. Baseline demographic, laboratory, and clinic characteristics were evaluated between the two groups. Logistic regression analysis was used to identify independent predictors of CIN. Results: The receiver operating characteristic curve analysis demonstrated that the optimal cutoff value of SII for predicting CIN was 1,282 with a sensitivity of 76.1% and specificity of 86.7% (AUC: 0.834; 95% CI: 0.803-0.863; p < 0.001). Multivariate analysis performed in two models (SII; as separate continuous and categorical variables) showed age, estimated glomerular filtration rate (eGFR), diabetes, left ventricular ejection fraction (LVEF), Killip class >= 2, use of an intravenous diuretic, troponin I, and SII as independent predictors of CIN in model 1. In model 2, age, eGFR, diabetes, LVEF, Killip class >= 2, use of an intravenous diuretic, troponin I, and a value of SII >1,282 (p < 0.001, OR 6.205, 95% CI: 2.301-12.552) remained as independent predictors of CIN. Conclusion: SII may be a useful and reliable indicator to predict the development of CIN in patients with STEMI undergoing primary PCI than NLR and PLR.