Acute kidney injury (AKI) is associated with both short- and long-term clinical consequences including progression to chronic kidney disease. Recovery of renal function has gained importance, as interventions to prevent or treat AKI are limited. Basing recovery on a return of serum creatinine values excludes mounting evidence that AKI, even when reversible, is a very serious clinical event that will result in a significant number of both renal and extra-renal complications such as late stage kidney disease, major cardiovascular events, and death.Development of a definition for renal recovery is critical to organizing research in AKI treatment. Assessment of serum creatinine remains the primary measure of renal recovery despite known limitations. Patterns of renal recovery are highly associated with clinical outcomes including survival. Additional research in basic mechanisms of renal injury and repair is needed to help formulate a more comprehensive assessment of renal recovery. Novel biomarkers for assessment of AKI may also aid in the determination of renal recovery. Key Messages: (1) The concept of acute kidney disease (7-90 days post AKI) should direct clinicians as well as researchers to pay attention to a critical time period for renal recovery in which interventions may alter long-term outcomes. (2) Recent studies have evaluated AKI recovery patterns, or trajectories, and is an important step towards defining long-term prognosis. (3) Serum creatinine alone is not a reliable marker of recovery after AKI and is associated with poor clinical outcomes despite a return to baseline levels. This is a work of the U.S. Government and is not subject to copyright protection in the United States. Foreign copyrights may apply. Published by S. Karger AG, Basel.