Familial hypercholesterolemia (FH) is among the most common single-gene diseases and is due to mutations of the low-density lipoprotein (LDL) receptor gene. In heterozygous FH, serum LDL-cholesterol level is elevated two- to threefold compared to unaffected individuals, men in particular are prone to premature atherosclerosis and early cardiac deaths. However, very little data are available concerning the incidence of premature deaths in FH patients. In Finland two LDL receptor founder mutations cover two-thirds of FH cases, offering a unique possibility to study the potential role of FH in unexpected early cardiac deaths. We studied a total of 149 deceased who had suffered early (< or = 50 years) unexpected cardiac death due to coronary heart disease (CHD). Three individuals (2%) had molecularly defined heterozygous FH, and heterozygous FH was present in two (3%) of the 67 subjects who had demonstrable acute myocardial infarction (AMI). Considering that the two FH mutations cover two-thirds of FH cases in Finland, the overall prevalence of FH underlying early cardiac deaths caused by AMI may be estimated to be in the range 3 to 5%.