Background We aimed to evaluate prevalence of acute kidney injury (AKI) and its risk factors in children hospitalized for acute gastroenteritis (AGE) to identify early predictors of AKI. Methods We retrospectively collected clinical and biochemical data of 114 children (57.9% male; mean age 2.9 ± 2.8 years) hospitalized for AGE. AKI was defined according to Kidney Disease/Improving Global Outcomes creatinine criteria. We considered basal serum creatinine as value of creatinine estimated with Hoste (age) equation assuming basal eGFRs were median age-based eGFR normative values for children ≤ 2 years of age, and eGFR 120 mL/min/1.73m 2 for children > 2 years. Univariate and multivariate logistic regression models were used to explore associations with AKI. We included in multivariate analyses only variables with significant p after Bonferroni correction. Results AKI was found in 28/114 (24.6%) patients. No patients required hemodialysis, 2 (1.8%) reached AKI stage 3, 2 (1.8%) AKI stage 2, and 24 (21.0%) AKI stage 1. Mean length of stay was 3.6 ± 1.2, 5.0 ± 1.8, and 10.5 ± 5.8 days, for patients with no, mild, and severe AKI ( p < 0.001), respectively. Duration of symptoms before hospitalization (OR = 2.5; 95% CI = 1.3–5.0; p = 0.006), dehydration > 5% (OR = 43.1; 95% CI = 5.4–344.1; p = < 0.001), and serum bicarbonate levels (OR = 1.6; 95% CI = 1.2–2.1; p = 0.001) were independent predictors of AKI. Conclusions About one quarter of patients hospitalized for AGE may suffer from AKI with a longer stay for patients with more severe AKI. Particular attention, however, should be paid to volemia and kidney health of patients with AGE especially in the presence of increased duration of symptoms before hospitalization, dehydration, and lower serum bicarbonate levels. Graphical abstract