PURPOSE: We aimed to study the clinical characteristics, courses, and outcomes of critically ill patients with septic acute kidney injury (AKI) treated with continuous renal replacement therapy (CRRT) in comparison with nonseptic AKI treated with CRRT. METHODS: This is a multicenter retrospective observational study conducted in 14 Japanese intensive care units in 2010. All adult patients with severe AKI treated with CRRT were eligible (n = 343), and information on patient characteristics, variables at CRRT initiation, CRRT settings, and outcomes was collected. Patients were categorized into the septic AKI group and the nonseptic AKI group according to contributing factors to AKI. RESULTS: Approximately half of study patients (48.7%) had sepsis/septic shock as a contributing factor to AKI, and patients with septic AKI treated with CRRT had more serious clinical conditions than patients with nonseptic AKI. However, no significant difference was observed in intensive care unit mortality (48.5% vs 43.8%; P = .44) and hospital mortality (61.1% vs 56.3%; P = .42) between patients with septic and nonseptic AKIs treated with CRRT. Furthermore, sepsis was associated with lower hospital mortality (odds ratio, 0.378; P = .012) in multivariable regression analysis. CONCLUSION: Sepsis may not be a risk factor for mortality in patients with AKI whose condition has become severe enough to require CRRT.