A cohort of 4 475 Finnish men was followed up during 1964-80 in order to study regional differences in mortality from cardiovascular diseases, especially ischaemic heart disease (IHD). The west/east gradient in cardiovascular mortality recorded in several previous studies was greatly age-dependent. The excess eastern risk was a feature of younger age groups; with increasing age the risk pattern was reversed. The risk factors in IHD in eastern Finland have an element which somehow accelerates the process of this disease.