Creutzfeldt-Jakob disease (CJD) belongs to a group of transmissible spongiform encephalopathies in which neuropathological confirmation is needed for a definite diagnosis. Based on clinical symptoms, the disease can be characterized only as possible or probable. The diagnostic criteria for sporadic CJD (sCJD) approved by the World Health Organization include 14-3-3 protein as a marker detectable in the cerebrospinal fluid (CSF). Since 2010, also magnetic resonance FLAIR or DWI imaging has been included in the criteria for sCJD. 14-3-3 protein is a normal neuronal protein released to the CSF as a result of extensive neuronal damage. As it is a non-specific marker, a positive result gives no information about the reason of the neuronal death. The test for 14-3-3 protein is useful only when considered in an appropriate clinical context, together with other diagnostic criteria. In certain conditions, false negative as well as false positive results are possible. The 14-3-3 protein is detected in about 90% of sporadic CJD cases, whereas the result is positive in only 50% of variant CJD patients, therefore this analysis is less useful in the diagnostics of vCJD.