Variant Creutzfeldt-Jakob disease (vCJD) is an emerging infectious disease believed to be the human manifestation of bovine spongiform encephalopathy (BSE). Variant CJD belongs to a family of human and animal diseases called transmissible spongiform encephalopathies (TSE). The pathogenesis of TSE is not fully understood, but a modified form of a normal cellular protein plays a central role. Current measures to control vCJD aim to prevent transmission of the infectious agent from animals to humans through food or pharmaceutical products and to prevent transmission from person to person via medical interventions. The anticipated development of preclinical diagnostic tests and treatments for vCJD will create new control options and difficult choices.