This Review covers the rationale, physiological consequences and clinical application of pharmacological sodium-glucose cotransporter 2 (SGLT2) inhibition. In patients with type 2 diabetes mellitus, in whom renal glucose reabsorption might be upregulated, orally active, selective SGLT2 inhibitors improve glycaemic control to a therapeutically useful extent. Chronic administration of several SGLT2 inhibitors dose-dependently lowers HbA(1c) levels by 0.5-1.5% without causing hypoglycaemia. The unique mechanism of action of SGLT2 inhibitors-which does not hinge upon β-cell function or tissue insulin sensitivity-means that they can exert their antihyperglycaemic effects in combination with any other oral antidiabetic drug as well as insulin. Available phase III studies confirm a good tolerability profile. Weight loss owing to urinary calorie leakage may be less than expected, but the negative energy balance offers a valuable clinical benefit. Offloading of sodium can assist blood pressure control. The progressive loss of efficacy in patients with reduced glomerular function will have to be balanced against the possibility of renal protection. The safety issues of genitourinary infections and cancer risk requires careful, proactive monitoring and analysis of robust exposure data, particularly in elderly, frail patients and in patients with impaired kidney function and/or high cardiovascular/cancer risk, who represent an increasing fraction of the population with diabetes mellitus.