Objectives: To study the incidence, clinical characteristics, and prognostic impact of acute kidney injury (AKI) in very elderly patients. Methods: The very elderly patients (≥75 years) from the Geriatric Department of the Chinese PLA General Hospital between January 2007 and December 2015 were retrospectively enrolled. AKI was defined according to the 2012 Kidney Disease Improving Global Outcomes (KDIGO) criteria. AKI patients were divided into survivor group and non-survivor group by their outcomes within 90 days after AKI. Prognostic survival factors were identified using the Cox proportional hazards regression model. Results: In total, 668 geriatric patients (39.0%) developed AKI, and 652 patients were included in the final analysis. The median age of the cohort was 87 (84-91) years, the majority (623 cases, 95.6%) of whom were male. Among these 652 patients, 308 (47.2%) had AKI stage 1, 164 (25.2%) had AKI stage 2, and 180 (27.6%) had AKI stage 3. Of the 652 AKI patients, the 90-day mortality was 33.6% (219/652). Multivariate analysis by the Cox model revealed that persistent AKI (HR=5.741, 95% CI: 3.356-9.822, P<0.001), more severe AKI stage (stage 2: HR=3.363, 95% CI: 1.973-5.732, P<0.001 and stage 3: HR=4.741, 95% CI: 2.807-8.008, P<0.001), high blood urea nitrogen (BUN) level (HR=1.025, 95% CI: 1.014-1.037, P<0.001), low body mass index (HR=0.939, 95% CI: 0.897-0.984, P=0.008), low mean arterial pressure (MAP) (HR=0.969, 95% CI: 0.959-0.979, P<0.001), low prealbumin level (HR=0.935, 95% CI: 0.911-0.959, P<0.001), infection (HR=1.410, 95% CI: 1.055-1.884, P=0.020), oliguria (HR=1.948, 95% CI: 1.266-2.998, P=0.002) were associated with 90-day mortality. Conclusions: The incidence of AKI increases significantly with advanced age. More frequent serum creatinine (SCr) measurements may be helpful for the early diagnosis of geriatric AKI. Identification of risk factors might promote more intensive monitoring and early prevention, and thus improve outcomes for very elderly patients with AKI.