BACKGROUND: Nonsteroidal anti-inflammatory drugs (NSAIDs) are a frequently prescribed class of medications in the neonatal intensive care unit (NICU). We aimed to reveal acute kidney injury (AKI) epidemiology in NSAID-exposed premature infants admitted to the NICU using a standardized definition and determine the percentage of NSAID-exposed patients with adequate serum creatinine (SCr) monitoring. METHODS: This retrospective study compared infants born at ≤34 weeks gestational age who received NSAID for intraventricular hemorrhage prophylaxis (prophylaxis group) or symptomatic treatment for patent ductus arteriosus (PDA; treatment group) between January and December 2014 at a tertiary NICU. All available SCr and 12-h urine output (UO) values were recorded from admission until day seven post-NSAID exposure. AKI incidence was determined using the neonatal modified Kidney Disease Improving Global Outcomes classification, defined as an increase in SCr (i.e., 1.5 fold rise from previous SCr measurement within seven days or 26.5 mmol/L increase within 48 h) or UO < 1 mL/kg/hour, excluding the first 24 h of life. RESULTS: We identified 70 eligible subjects; 32 received prophylactic NSAIDs, and 38 received indomethacin or ibuprofen for treating symptomatic PDA. AKI incidence for the entire cohort was 23% (16/70). The prophylaxis group had a significantly lower AKI rate than the treatment group (9% vs. 34%; p = 0.014). The treatment group had a higher proportion of infants with adequate SCr monitoring during NSAID treatment than the prophylaxis group (87% vs. 13%, p < 0.001). CONCLUSION: NSAID-associated AKI occurred in approximately one-quarter of premature infants overall, and the AKI incidence was higher in infants treated with NSAIDs for the symptomatic treatment of PDA than in those receiving prophylactic treatment during the first day of life. Standardized protocols for monitoring daily SCr and UO after exposure should be implemented for all neonates with NSAID exposure to improve early AKI recognition and management.