Aim To assess the proportion of patients, aged 40 years and over, attending an inner city accident and emergency department that have Type 2 diabetes, and the proportion previously undiagnosed, and to assess whether the identification of undiagnosed Type 2 diabetes is feasible in this setting. Methods Five hundred unselected people participated. All completed a demographic questionnaire regarding risk factors for diabetes. In those without known diabetes, random capillary blood glucose (CBG) was measured. If this was greater than 7.0 mmol/l, patients were asked to return for two fasting blood glucose tests. Diagnosis of diabetes was based on World Health Organization criteria. Results Of the 500 participating subjects, 73 were already known to have Type 2 diabetes. Of the remaining 427 subjects, 36 had CBG > 7.0 mmol/l. All 36 returned for fasting blood tests: 13 fulfilled the diagnostic criteria for Type 2 diabetes, eight for impaired fasting glucose (IFG), and 15 had normal fasting glucose values. The prevalence of Type 2 diabetes was therefore 17.2%, including 2.6% with a new diagnosis, and 14.6% with pre-existing disease; 1.6% were found to have IFG. Body mass index was greater in those with Type 2 diabetes (previously and newly diagnosed) [27.1 (5.15) (mean +/- standard deviation)] vs. 25.8 (4.70) kg/m(2); unpaired t-test P = 0.0213), and those with Type 2 diabetes were more likely to be of black and minority ethnic origin (57 vs. 28%; chi P-2 < 0.001) and to have a first-degree family history of diabetes (45 vs. 23%; chi P-2 < 0.001). Conclusions It can be estimated from this survey that, annually, this case-finding methodology could identify 539 (95% CI 249-828) people aged 40 years and over attending our accident and emergency department with previously undiagnosed Type 2 diabetes.