Prion diseases comprise a group of diseases characterised by transmissibility, spongiosis, gliosis, neuronal loss, and accumulation of an abnormally folded membrane protein, PrP(Sc). Infectivity resists almost all chemical and physical processes that inactivate conventional viruses, whereas protein extraction abolishes infectivity. This fact is of great importance to surgery, especially neurosurgery, since conventional cleaning of surgical instruments does not abolish infectivity. As a matter of consequence, few cases of putative neurosurgical transmission of Creutzfeldt-Jakob disease (CJD) have been reported. Putative transmission has also been reported through the use of lyophilised dura mater, corneal transplants, and cortical EEG electrodes. Moreover, many children have been infected with CJD by intramuscular or subcutaneous injection of cadaveric pituitary-derived human growth hormone. In recent years, the occurrence of bovine spongiform encephalopathy and consequently new variant Creutzfeldt-Jakob disease has increased concerns that prions also may contaminate the blood supply. Animal models of prion disease can help the understanding of how prions spread within an infected organism and the identification of which tissues may be contagious. Taking the right precautions against iatrogenic transmission requires knowledge about the nature of prion diseases - not only for the persons working out the directives but also for health care workers potentially involved with CJD patients or contaminated specimens.