Prion diseases are uncommon fatal neurodegenerative disorders that have gained scientific importance as a result of the emergence of new forms of these diseases in both animals and humans. Prions appear to be composed principally or entirely of abnormal isoforms of a host-encoded glycoprotein. There is substantial scientific evidence to support the notion that bovine spongiform encephalopathy (“mad cow disease”) has affected humans. Recent studies have demonstrated that prions can adhere easily to metal surfaces, and normal sterilization procedures are not likely to completely inactivate them. Iatrogenic transmission of prion diseases, such as Creutzfeldt-Jakob disease, was recognized after corneal transplantations, dura mater grafts, neurosurgical procedures, and the use of human hormones (growth hormone and gonadotropin). Although bovine collagen has long been recognized as a safe and biocompatible material, dermatologists should be aware of the theoretical potential for prion transmission when materials from bovine origin and products obtained from cultured cells fed with fetal or newborn calf serum are used. (J Am Acad Dermatol 2002;46:790-3.)