Since reports of the mad cow disease epidemic in Great Britain erupted in the international press, sensational and intimidating articles about the risk that bovine spongiform encephalopathy and related diseases may pose to humans have appeared. The bad news is that compelling scientif ic evidence suggests so-called prion disease can and has infected humans, although the overall risk appears to be low. Furthermore, at present, there is no reliable antemortem diagnosis, specific treatment, or vaccine to prevent the disease. The agent thought to be responsible for this unusal class of disease is a rogue protein (called a prion) that, unlike all other agents known to cause infectious disease, contains neither DNA nor RNA. According to a popular hypothesis, normal membrane-associated prion proteins undergo conformational changes that can cause disease. The bad prion forms cause holes or a spongy appearance in the brain in all disease variants, hence the generic designation of spongiform encephalopathy. The good news is that risk for exposure to prion disease is exceedingly remote in the dental practice and that current universal infection control procedures are probably sufficient.