About 20% of all adult emergency admissions are affected by acute kidney injury (AKI) and the mortality rate is almost 25%. It has been estimated that AKI, excluding cases in the community, causes more than 10,000 preventable deaths a year in England. AKI represents a wide spectrum of injury to the kidneys, not just kidney failure, the vast majority of AKI cases start with an illness in the community. In AKI, loss of kidney function contributes to morbidity and mortality. Patients die from AKI rather than with AKI as a complication of an underlying illness. The diagnosis of AKI is currently based on a rise in creatinine, and/or reduced urine output, eGFR is not used in diagnosis. AKI may only be seen as a small rise in creatinine. The rise needs to be on a short, acute timescale to distinguish it from the slower steady rise of progressive chronic kidney disease (CKD). AKI episodes are common in patients with CKD. Such episodes are an important factor in the progression of CKD. The definition of AKI now includes any adult with > or = 26 micromol/L rise in creatinine from baseline over 48 hours or less, or > or = 50% rise in creatinine from baseline known or presumed to have occurred over seven days or less. In patients with known or suspected AKI all nephrotoxic drugs should be suspended. The use of NSAIDs should be avoided, ACE inhibitors and angiotensin receptor blockers should be suspended during any episode of vomiting and/or diarrhoea.