PURPOSE: To determine the proportion of diagnosis and outcomes of critically ill patients with acute kidney injury (AKI), and its association with mortality using the complete Kidney Disease Improving Global Outcomes (KDIGO) classification and Sepsis-3 definition. METHODS: We conducted a multicenter prospective cohort study of 13 intensive care units (ICU) in Japan. Patients admitted to the ICUs during six months in 2016 were consecutively enrolled. RESULTS: Among 2292 patients, AKI was diagnosed in 1024 (44.7%) patients, using the KDIGO classification. Sepsis was diagnosed in 424 patients (18.5%), of whom 281 patients (66.3%) had AKI. Septic shock was diagnosed in 166 patients (7.2%), of whom 125 patients (75.3%) had AKI. Of 1024 patients with AKI, renal replacement therapy was applied to 171 patients (16.7% of AKI) during the ICU stay. The adjusted odds ratio (aOR) of AKI to hospital mortality was 1.66 (95% confidence intervals 1.26-2.18), while that among sepsis was 0.87 (95% confidence intervals 0.55-1.37). CONCLUSIONS: AKI accounted for >40% of ICU patients with the KDIGO classification and was associated with increased risk of hospital mortality. Septic AKI was diagnosed in three-fourths of patients with sepsis, while the impact of AKI on hospital mortality among sepsis was not observed.