Common polymorphisms of the fibrinogen gene cluster are associated with circulating fibrinogen level and with susceptibility to and/or severity of atherothrombotic disease. The frequencies of the polymorphisms vary among different ethnic groups but there is strong linkage disequilibrium at the beta-fibrinogen gene locus so that, in caucasian populations, there are only four common beta-fibrinogen haplotypes. One of these haplotypes, defined by the beta-fibrinogen -455A allele, is associated with elevated fibrinogen level and increased risk of atherothrombotic disease. The molecular mechanism of these associations is currently under investigation.