OBJECTIVE--To analyse anthropometric and metabolic characteristics as risk factors for development of non-insulin dependent diabetes mellitus in middle aged normoglycaemic men. DESIGN--Prospective population study based on data collected in a health survey and follow up 10 years later. SETTING--Uppsala, a middle sized city in Sweden. SUBJECTS--2322 men aged 47-53, of whom 1860 attended the follow up 7-14 years later, at which time they were aged 56-64. MAIN OUTCOME MEASURES--Incidence of non-insulin dependent diabetes. RESULTS--In a multivariate logistic regression analysis, variations of 1 SD from the mean of the group that remained euglycaemic were used to calculate odds ratios and 95% confidence intervals. Blood glucose concentration 60 minutes after the start of an intravenous glucose tolerance test (odds ratio = 5.93, 95% confidence interval 3.05 to 11.5), fasting serum insulin concentration (2.12, 1.54 to 2.93), acute insulin increment at an intravenous glucose tolerance test (1.71, 1.21 to 2.43), body mass index (1.41, 1.01 to 1.97), and systolic blood pressure (1.23, 0.97 to 1.56) were independent predictors of diabetes. In addition, the use of antihypertensive drugs at follow up (selective or unselective beta blocking agents, thiazides, or hydralazine) was an independent risk factor (1.70, 1.11 to 2.60). CONCLUSIONS--Metabolic and anthropometric characteristics associated with or reflecting insulin resistance as well as a poor acute insulin response to glucose challenge were important predictors of future diabetes in middle aged men. Antihypertensive drugs were found to constitute a further, iatrogenic risk factor.