The prevalence of diabetes mellitus increases with advancing age but often remains undiagnosed. We examined the use of a blood glucose assay, performed on admission in 515 consecutive acute admissions, aged 65 years and over as an initial screening test for diabetes mellitus. Of these, 7.6% were previously known to have diabetes and 4.7% were newly diagnosed on the basis of subsequent fasting blood glucose estimations. Using a random blood glucose level ≥8.0mmol/1, 18.5% of those screened needed further investigation. Although this method has been used for many years to screen for diabetes a formal comparison with a glucose tolerance test is needed before it can be used as the sole screening test.