Vitamin D status was assessed in 142 elderly Dutchmen participating in a prospective population-based study of environmental factors in the aetiology of non-insulin-dependent diabetes mellitus. Of the men aged 70-88 years examined between March and May 1990, 39% were vitamin D depleted. After adjustment for confounding by age, BMI, physical activity, month of sampling, cigarette smoking and alcohol intake the 1-h glucose and area under the glucose curve during a standard 75-g oral glucose tolerance test (OGTT) were inversely associated with the serum concentration of 25-OH vitamin D (r = -0.23, p < 0.01; r = -0.26, p < 0.01, respectively). After excluding newly diagnosed diabetic patients total insulin concentrations during OGTT were also inversely associated with the concentration of 25-OH vitamin D (r = -0.18 to -0.23, p < 0.05). Hypovitaminosis D may be a significant risk factor for glucose intolerance.