The aim of this cross-sectional study was to describe the prevalence of total, known and unknown diabetes mellitus and impaired fasting glucose (IFG) in the population of Murcia (SE Spain), a Mediterranean area with a high prevalence of obesity. Therefore, 2562 subjects (>or=20 years) were selected by stratified random sampling and a survey was carried out by telephone, together with a physical examination and biochemical determinations. The ADA-1997 diagnostic criteria were used. The crude prevalence of total diabetes was 11% (9.5-12.6%), known diabetes 7.8% (6.5-9.2%), unknown diabetes 3.2% (2.4-4.2%) and IFG 4.9% (3.9-6.1%). Both total diabetes and IFG were higher in men than in women, with prevalence rates increasing with age. People with diabetes and IFG had higher BMI, blood pressure, total cholesterol, LDL-cholesterol and triglyceride values than the rest of the population. No difference in the prevalence of diabetes was observed between the rural and urban populations. The prevalence of diabetes in Murcia is high compared to the rest of Spain and the world, suggesting that the possible benefits attributed to some characteristics of the diet of this Mediterranean population are not sufficient to counteract the risk factors associated with the disease.