In the first part of this work the main problems of prion diseases--also called transmissible cerebral amyloidoses (TCA) or subacute (transmissible) encephalopathies (SSE, TSE)--and clinical symptoms of Creutzfeldt-Jakob disease are presented. Some problems of neuropathology of Creutzfeldt-Jakob disease and basic informations about other human prion diseases will be presented in the second part. The growth of the interest in prion diseases during last years is caused by the problem of bovine spongiform encephalopathy (BSE or "mad cow disease") and its transmission into a human. The new variant of Creutzfeldt-Jakob disease (nvCJD) has appeared. Prion diseases: Gerstmann-Sträussler-Scheinker syndrome (GSS), kuru, fatal familial insomnia (FFI) and particularly the most frequent of them--Creutzfeldt-Jakob disease (CJD)--have nonspecific, sometimes variable clinical (psychopathological and neurological) symptoms. The imaging, EEG, cerebrospinal fluid tests and other laboratory tests are not specific either and their diagnostic value is limited. Neuropathological studies are needed but their interpretation is often difficult. The only certain diagnostic marker for TSE is the presence of PrP(Sc), the prion protein, which is presently believed to be a direct cause for all transmissible cerebral amyloidoses (TCA).