Prion diseases, or transmissible spongiform encephalopathies, are a group of neurodegenerative diseases with progressive dementia and movement disorders. There are three variants of prion diseases pathogenesis: direct contamination, genetic and sporadic forms. The following clinical forms are known: Creutzfeldt—Jakob disease (common type), variant Creutzfeldt—Jakob disease, Gerstmann-Straussler-Scheinker disease, variably protease-sensitive prionopathy, fatal insomnia and fatal familial insomnia, kuru, prion disease associated with diarrhea and autonomic neuropathy. Clinical characteristic of prion diseases, molecular-genetic aspects of their pathogenesis and current diagnostic approaches are discussed. Because of the lack of effective treatment, prevention of both alimentary prion infections (consumption of contaminated meat products) and transmissible iatrogenic infections (the use of biopreparations from animal tissues) is important. The safety of such biopreparations should be ensured by modern manufacturing technologies and specially developed procedures that meet international requirements and standards.