Background: Acute kidney injury (AKI) is common in critically ill children and is associated with poor outcome. Objective: To study the incidence, risk factors and outcome of AKI in children admitted to paediatric intensive care unit (PICU) of a developing country. Materials and Methods: This prospective observational study was conducted in a tertiary care PICU over one-year period. Critically ill children aged from 2 months to 18 years were included. RIFLE criteria based on GFR, and urine output was used for categorisation. Results: Of 380 children, 53 children (14%) had AKI (met any of the RIFLE criteria). The most common diagnoses underlying AKI were acute lower respiratory tract infection, CNS illness and severe dehydration. Subjects with AKI had a higher PRISM score (>10) at admission, longer duration of stay and high mortality. Significant risk factors for AKI following multivariate analysis were: age 1-5, PRISM score (>10) at admission, shock, infection, thrombocytopenia, hypo-albuminaemia and multi-organ dysfunction. Twenty-six of 53 subjects fulfilled the maximum RIFLE criteria within 72 h after admission and the mean (SD) time to first RIFLE attend was 1.6 (1.2) day. Subjects with AKI (RIFLE criteria) had 4.5 times higher mortality than those without AKI (36 vs 8%, P< etc). Conclusion: A high incidence of AKI was noted in the PICU that was associated with high mortality. The RIFLE criterion is an effective tool which can be used not only for predicting the outcomes, but may help in the early identification of patients at risk for AKI.