Cross sectional and prospective surveys of thyroid autoimmunity have been performed in two cohorts of men, 280 living in west Finland and 269 in east Finland. In both populations, aged 50 to 69 years at the first survey, risk factors for coronary heart-disease (C.H.D.) were common. The incidence of C.H.D. was shown to be related to the presence of thyroid antibodies. The results of the cross-sectional studies were not conclusive. The five-year follow-up study emphasised that in both areas asymptomatic thyroid autoimmunity, independently of other known risk factors, was a predictor of subsequent development of C.H.D. The importance of asymptomatic autoimmune thyroid-itis as a risk factor for C.H.D. increases with age.