The last 10 years have seen the emergence of a new disease termed variant CJD. This disease is thought to be initiated by abnormal prion proteins. This article reviews the different clinical manifestations of human prion diseases and provides some background information on the biological nature of this unique infectious agent. Prion proteins present a challenge to infection control because of their relative resistance to the conventional sterilization process. This article highlights the issues involved and discusses current guidelines for management of patients with human transmissible encephalopathies.