Gestational diabetes mellitus is defined as carbohydrate intolerance of variable severity with onset or first recognition during pregnancy. It has been shown that the risk of adverse maternal, foetal, and neonatal outcomes in gestational diabetes mellitus is related to the degree of glucose intolerance and/or hyperglycaemia; gestational diabetes mellitus also has long-term sequelae for both the mother and the offspring. As gestational diabetes mellitus is rarely symptomatic, diagnosis of the condition relies on screening. The diagnostic criteria and the management of gestational diabetes mellitus are discussed and areas of controversy and recent advances highlighted.