The clinical diagnosis of Creutzfeldt-Jakob disease (CJD) is often difficult, since the clinical presentation varies between patients and is often uncharacteristic. Therefore, CJD is often not suspected until late in the disease process, due to the rapid progress of the disease. Suspected CJD is, however, frequent in routine clinical practice, in the investigation of patients with rapidly progressing dementia and/or uncharacteristic neurological symptoms. We present results from cerebrospinal fluid (CSF) analyses in CJD, focusing on the two neuron-specific proteins 14-3-3 and tau. Analysis of 14-3-3 protein is performed by Western blotting, in which 14-3-3 is either detectable in CSF or not, while CSF-tau is analyzed using quantitative ELISA methodology, in which a markedly increased CSF level of tau (< 1500 pg/mL) is indicative of CJD. Tau and 14-3-3 findings show comparable sensitivity and specificity, higher than the presence of spike and wave complexes on an EEG. The increase in CSF-tau in CJD is substantially higher than in Alzheimer's disease, with low overlap between the disorders. Instead, false positive results are found in disorders with massive acute neuronal damage (encephalitis, stroke and CNS tumors). In cases in which these disorders cannot be differentiated from CJD on clinical grounds, they can often be identified by MRT or by the finding of blood-brain barrier damage or signs of inflammation upon CSF analysis. CSF-tau is increasingly used in the routine diagnosis of Alzheimer's disease, and the analysis also seems to be of use in the clinical diagnosis of CJD. We also present three cases from routine clinical practice, all with a marked increase in CSF-tau, which was the only positive objective sign in two of the cases.