Background: Acute kidney injury (AKI) is a frequent postoperative (PO) complication for cardiac surgery; however, its co-incidence after non-cardiac surgery (NCS) is indefinite. Objectives: To determine the predictors for postoperative (PO-AKI) among patients undergoing NCS. Patients: 413 patients aged >40-y underwent NCS procedures requiring longer than 1h and 205 patients underwent CABG surgery as a control group for AKI incidence only. Blood samples were obtained for the estimation of serum creatinine and calculation of the neutrophil/lymphocyte ratio (NLR). All patients received general inhalational anesthesia according to the surgical procedure. PO-AKI was diagnosed according to the guidelines of the European Renal Best Practice. Study outcomes included the incidence of PO-AKI and its relation to patient's data. Results: The incidence of PO-AKI was 10.4% and AKI patients were significantly older, obese and had lower preoperative hemoglobin concentration (HBC). Seven patients (1.7%) required packed RBCs transfusion and 32 patients (7.7%) developed intraoperative hypotension (IOH) with significantly lower frequencies among No-AKI patients. The NLR was significantly higher in samples of AKI than in No-AKI patients. Regression analysis defined NLR and IOH as significant predictors for PO-AKI. Paired-Sample analysis showed a significant (P=0.01) difference between the area under the curve in favor of NLR. Conclusion: AKI after is more frequent among older obese patients with low HBC. Excessive blood loss, IOH and long operative time increased the risk of PO-AKI. Preoperative NLR showed high predictive performance for PO-AKI and might be considered as promising routine, cheap and feasible test for distinguishing patients vulnerable to develop AKI.