Acute kidney injury (AKI) is a common complication in hospitalised patients and is associated with an increased risk of chronic kidney disease (CKD) and higher mortality. Two thirds of AKI cases develop in the community prior to hospital admission. AKI may be challenging to recognise because it is typically asymptomatic. It is usually detected incidentally in the setting of another illness when a rise in serum creatinine from baseline is identified. Risk factors for AKI include age 65 or over, diabetes, CKD, neurological or cognitive impairment, heart failure and the use of potentially nephrotoxic medications. Recognition of those at risk should prompt earlier and more frequent testing of U&E during any acute illness.