Acute interstitial nephritis (AIN) is a rare, often underdiagnosed condition and a common cause of renal failure. Drugs are the leading cause. The underlying pathophysiological condition is often a type IV hypersensitivity reaction. There are also rarer idiopathic forms, which often remain unrecognized. Additionally, the pathophysiological mechanisms are poorly understood, so that only very few promising forms of treatment are available. For some medications the overall risk is low but the side effects are relevant for the clinical routine due to the fact that they are frequently prescribed. In addition, the development of new approaches, such as immunotherapy also leads to side effects that cannot be completely predicted. For many diseases the occurrence of acute kidney injury increases the mortality and morbidity. A potentially irreversible chronic renal failure increases the incidence of further comorbidities and reduces the quality of life. Treatment is difficult and mostly empirical.