Background: Anemia on admission is associated with an increased risk for contrast-induced nephropathy, however, its association with acute kidney injury (AKI) after ST segment elevation myocardial infarction (STEMI) in patients undergoing primary percutaneous coronary intervention (PPCI) has not been studied. Our aim was to evaluate whether admission hemoglobin levels might increase the risk of AKI among STEMI patients who undergo PPCI. Methods: We performed a retrospective analysis of 1248 consecutive patients admitted with the diagnosis of STEMI between January 2008 and January 2014, and treated with PPCI. Patient medical records were reviewed for admission hemoglobin levels and for the occurrence of AKI. Results: The mean age of patients was 61 ± 13 years and 1009 (81%) were male. AKI occurred in 115 patients (9.2%). Patients with AKI were more likely to be older, female, with more comorbidities, had longer symptom duration, and more likely to be in a critical state. Patients with AKI had significantly lower admission hemoglobin levels (13.6 ± 1.7 g/dL vs 14.4 ± 1.5 g/dL; P < 0.001) and were more likely to be anemic (27% vs 12%; P < 0.001). In a multivariate logistic regression model, a lower admission hemoglobin level (odds ratio, 0.86; 95% confidence interval, 0.74-0.98; P = 0.04) and the presence of anemia on admission (odds ratio, 1.76; 95% confidence interval, 1.02-3.02; P = 0.04) emerged as independent predictors of AKI. Conclusions: Among STEMI patients who underwent PPCI, a lower admission level of hemoglobin and anemia (hemoglobin < 12 in women or < 13 in men) were independent predictors of AKI. Precautions to prevent AKI should be particularly considered in anemic patients.