BACKGROUND: Acute kidney injury (AKI) is a significant cause of morbidity and mortality for critically injured trauma patients. The Kidney Disease: Improving Global Outcomes (KDIGO) practice guideline is the most up-to-date classification for AKI. The aims of this study were to determine the incidence and risk factors for AKI in critically injured trauma patients using the current KDIGO definitions. STUDY DESIGN: A prospective cohort study was performed at our academic, level 1 trauma center, from September 2017 to August 2018. All adult trauma patients admitted to the surgical ICU were included. The primary outcome was the development of AKI, as defined by KDIGO. Secondary outcomes included hospital and ICU length of stay, ventilator days, and mortality. RESULTS: There were 466 patients included and 314 (67%) developed AKI. Those who developed AKI were more often hypotensive on admission (7% vs 2%), had higher Injury Severity Scores (ISS) (19 vs 13), were more likely to have severe injuries to the chest (40% vs 24%) and extremities (20% vs 6%), received transfusion (41% vs 21%), sustained crush injuries (8% vs 1%), received radiocontrast (75% vs 47%), nephrotoxic medication (74% vs 60%), or vasopressors (15% vs 3%). After multivariate analysis, risk factors independently associated with AKI include age, Injury Severity Score (ISS), severe extremity injuries, radiocontrast, and vasopressors. Those who developed AKI had higher mortality (9% vs 2%). CONCLUSIONS: Using current KDIGO criteria, the incidence of AKI in critically injured trauma patients was higher than previously reported. Older patients, with more severe injuries to their extremities and chest and who have suffered crush injuries, appear to be the most a risk. AKI in the critically injured patient results in an almost 5-fold increase in mortality.