To examine the contribution of cardiovascular risk factors to the development of non-insulin dependent diabetes mellitus, a prospective follow-up study was performed of a cohort, initially examined in a population survey on cardiovascular risk factors. The survey was conducted from 1975 to 1978 in the Netherlands among 5700 men and women aged 20 to 65. In 1988 a questionnaire on the prevalence of chronic diseases, including diabetes mellitus, was sent to all living participants of the initial survey. The general practitioners of the persons who indicated to have diabetes mellitus were asked to confirm the diagnosis. Diabetes mellitus was defined as current use of oral hypoglycemic drugs or insulin. After exclusion of the prevalent cases at the initial survey, 65 incident confirmed cases remained. All others responding to the questionnaire served as controls. The incidence of diabetes mellitus was associated with body mass index, use of diuretics, systolic and diastolic blood pressure. After adjustment for age and body mass index systolic and diastolic blood pressure were still associated with the incidence of non-insulin dependent diabetes mellitus in men; relative risks 1.28 (95% confidence interval 1.06-1.54) and 1.40 (95% CI 1.06-1.85) per 10 mmHg respectively. For women, only the relative risk associated with the use of diuretics remained statistically significant (2.26, 95% CI 1.04-4.90). This probably reflects the risk of (treated) hypertension: adjusted for blood pressure, the relative risk lost statistical significance. These findings suggest that elevated blood pressure is a risk for the development of non-insulin dependent diabetes mellitus (NIDDM). This supports the view that NIDDM and hypertension may have a similar origin.