Background: Acute kidney injury (AKI) commonly occurs in intensive care units (ICUs), leading to adverse clinical outcomes and increasing costs. However, there are limited epidemiological data of AKI in the critically ill in Beijing, China. Methods: In this prospective cohort study in 30 ICUs, we screened the patients up to 10 days after ICU admission. Characteristics and outcomes were compared between AKI and non-AKI, renal replacement therapy (RRT) and non-RRT patients. Nomograms of logistic regression and Cox regression were performed to examine potential risk factors for AKI and mortality. Results: A total of 3107 patients were included in the final analysis. The incidence of AKI was 51.0%; stages 1 to 3 accounted for 23.1, 11.8, and 15.7%, respectively. The majority (87.6%) of patients with AKI developed AKI on the first 4 days after admission to the ICU. A total of 281 patients were treated with RRT. Continuous RRT with predilution, citrate for anticoagulation and femoral vein for vascular access was the most common RRT pattern (29.9%, 84 of 281). Patients with AKI were associated with longer ICU-LOS and higher mortality and costs (P<0.001). In patients treated with RRT, 78.6 and 28.5% of RRTs were dependent on the 7th and 28th days, respectively. The 28 day mortalities of non-AKI, AKI stages 1-3, and septic shock patients were 6.83, 15.04, 27.99, 45.18 and 36.5%, respectively. Conclusions: Approximately half of our ICU patients experienced AKI. The majority of patients with AKI developed AKI during the first 4 days after admission to the ICU. Continuous RRT with predilution, citrate for anticoagulation and femoral vein for vascular access was the most common RRT pattern in our ICUs. AKI was associated with a higher mortality and costs, incomplete kidney recovery and s series of adverse outcomes.