Acute kidney injury (AKI) is associated with high morbidity and mortality and consumes substantial health-care resources, particularly when renal replacement therapy is required. Randomized controlled trials (RCTs) have not identified the optimal mode of renal replacement for AKI in terms of clinically relevant endpoints such as patient survival or recovery of renal function. As for other complex health interventions, the costs and consequences of AKI treatment are relevant to health-care providers and decision makers aiming to maximize health outcomes despite fixed health resources. Studies from several different centers suggest that continuous renal replacement therapy (CRRT) is more costly than intermittent hemodialysis and less economically attractive than even intensive intermittent dialysis. On the other hand, while the incremental costs of providing CRRT are significant, they remain relatively small compared with the projected costs of providing chronic dialysis to survivors who do not recover renal function. Even small differences in the risk of chronic dialysis in survivors are likely to determine the economic attractiveness of the different types of renal replacement therapies. To clarify the true incremental cost-effectiveness of these therapies, future RCTs should collect data on long-term survival, the need for chronic dialysis, and detailed information on costs.