In a cohort of 66 FH-men (age 25-55) prospectively recruited during a 2-years period, we estimated the incidence of coronary heart disease to 52% (N=34). Thirty-two percent (N=21) had earlier history of symptomatic ischaemic disease whereas 20% (N=13) had significant ST/T changes during exercise stress test. Amongst the 8 patients with positive exercise stress test who underwent coronary angiography, six had severe coronary artery disease. Because of the severity of the stenotic lesions, 4 of these 6 patients underwent coronary angioplasty or surgical bypass. We concluded that a great proportion of FH men suffered from myocardial ischaemia, either asymptomatic or symptomatic, and that even the silent form is associated with severe coronary stenosis. This advocates to systematically perform exercise testing in asymptomatic FH men after age 25.