The role and value of screening for diabetes mellitus is still unclear. If asymptomatic subjects are to be screened, then a fasting plasma glucose > 6.6 mmol l-1 or a venous plasma glucose 2 h after a 75 g oral glucose load > 8.0 mmol l-1 or the presence of any glucose in a urine sample passed 2 h after a main meal should be regarded as a positive result. A fasting plasma glucose in the range 5.5-6.6 mmol l-1 is an equivocal result which should lead to retesting in 6-12 months if there is any risk factor for diabetes (obesity, family history of diabetes, Asian/African racial origin). Other screening tests or combinations of tests are not recommended. Screening should be restricted to subjects between 40 and 75 years and should be undertaken only every 5 years (3 years if a risk factor for diabetes is present), ideally in parallel with other health screening test; subjects with a positive result should have further investigations as necessary to reach a diagnosis in line with WHO criteria.