The impact of risk factors for sudden and non-sudden coronary death was investigated in 3,589 Finnish men aged 40-59 years at entry from a prospective population survey. During a mean follow-up time of 11 years, 234 coronary deaths occurred, 150 of which were sudden, i.e. ensuing within 1 hour of the onset of symptoms. The severity of the manifestations of CHD at baseline investigation appeared to be a powerful predictor of sudden coronary death. Smoking and high serum cholesterol were significant predictors of sudden coronary death. High serum cholesterol was an equally significant predictor of sudden and non-sudden coronary death. High blood pressure did not appear to significantly increase sudden coronary death but increased the incidence of non-sudden death significantly. Obesity and diabetes did not appear to be independent risk factors for sudden coronary death. Smoking and high serum cholesterol were significant risk factors for sudden coronary death in men with manifestations of coronary heart disease. The results suggest that reduction of primary risk factors, especially smoking and high serum cholesterol, is important even after coronary heart disease has become manifest.