Background: The purpose of this Neonatal and Pediatric Heart and Renal Outcomes Network study was to describe the epidemiology and outcomes of cardiac surgery–associated acute kidney injury (CS-AKI) after cardiac surgery without cardiopulmonary bypass (non-CPB). Methods: We performed a retrospective study of neonates (≤30 days) who underwent non-CPB cardiac surgery at 22 centers affiliated with the Pediatric Cardiac Critical Care Consortium. CS-AKI was defined using the modified Kidney Disease: Improving Global Outcomes serum creatinine and urine output criteria from postoperative days 0 to 6. CS-AKI defined by serum creatinine was further subclassified into transient (resolved by postoperative day 3) and persistent/late (≥3 days). Multivariable regression analyses were used to determine risk factors for CS-AKI and associations with outcomes of ventilation hours and cardiac intensive care unit length of stay. Results: Five hundred eighty-two neonates (median age at surgery, 9 days [interquartile range, 5-15], 25% functional single ventricle] were included. CS-AKI occurred in 38.3%: Rate and severity varied across centers. Aggregate daily CS-AKI prevalence peaked on postoperative day 1 (17.1%). No stage of CS-AKI was associated with ventilation hours or length of stay. Persistent/late CS-AKI occurred in 48 patients (8%). Prostaglandin use and single-ventricle surgery were associated with persistent/late CS-AKI. Higher baseline serum creatinine but not persistent/late CS-AKI was associated with longer ventilation duration and intensive care unit length of stay after adjusting for confounders. Conclusions: Kidney Disease: Improving Global Outcomes–defined CS-AKI occurred commonly in neonates undergoing non-CPB cardiac surgery. However most CS-AKI was transient, and no CS-AKI classification was associated with worse outcomes. Further work is needed to determine the CS-AKI definition that best associates with outcomes in this cohort.