To estimate the prevalence of glucose intolerance in the elderly, oral glucose tolerance tests were performed as part of the Rotterdam Study, a population-based study in subjects aged 55 years and over. The study population consisted of 2,668 men and 3,950 women. Diabetes mellitus was defined as the use of antidiabetes medication, or a random or post-load serum glucose level of > or = 11.1 mmol/liter. Impaired glucose tolerance was defined as a post-load serum glucose between 7.8 and 11.1 mmol/liter. In men, the frequency of diabetes mellitus ranged from 5.9% in ages < 60 years to 19.8% in ages > 85 years, and in women from 3.8% in ages < 60 years to 18.9% in ages > 85 years; more than half of the subjects with diabetes were newly diagnosed. The prevalence of impaired glucose tolerance ranged from 8.8% and 11.0% in men and women aged < 60 years to 24.3% and 34.7% in men and women aged > 85 years. The prevalence of diabetes mellitus in the total Rotterdam Study population of 7,439 elderly men and women was estimated to be 11.3% (95% confidence interval (CI) 10.5-12.0). Waist/hip ratio, systolic blood pressure, hypertension, and number of cigarettes smoked increased with a worsening of the glucose tolerance from normal, hyperinsulinemia, impaired glucose tolerance to diabetes in both men and women (p < 0.01, adjusted for age). Body mass index was higher in subjects with glucose intolerance, but the frequency of obesity showed a relative decrease with worsening of glucose tolerance. These results show that glucose intolerance, especially impaired glucose tolerance and undetected diabetes mellitus, is common in the elderly. Moreover, not only subjects with diabetes mellitus but also subjects with hyperinsulinemia and impaired glucose tolerance have an increase of cardiovascular risk factors.