Acute kidney injury is a frequent and serious complication in hospitalized patients. Mortality rates have not substantially been decreased during the last 20 years. In most patients AKI results from transient renal hypoperfusion or ischemia. The consequences include tubular cell dysfunction/damage, inflammation of the organ, and post-ischemic microvasculopathy. The two latter events perpetuate kidney damage in AKI. Clinical manifestations result from diminished excretion of water, electrolytes, and endogenous / exogenous waste products. Patients are endangered by cardiovascular complications such as hypertension, heart failure, and arrhythmia. In addition, the whole organism may be affected by systemic toxification (uremia). The diagnostic approach in AKI involves several steps with renal biopsy inevitable in some patients. The current therapy focuses on preventing further kidney damage and on treatment of complications. Different pharmacological strategies have failed to significantly improve prognosis in AKI. If dialysis treatment becomes mandatory, intermittent and continuous renal replacement therapies are equally effective. Thus, new therapies are urgently needed in order to reduce short- and long-term outcome in AKI. In this respect, stem cell-based regimens may offer promising perspectives.