Background: The increase of the 14-3-3 protein in CSF is used as a diagnostic test in Creutzfeldt-Jakob disease (CJD), but the sensitivity and specificity of the 14-3-3 test are disputed. One reason for the dispute may be the recently established heterogeneity of sporadic CJD. The relationship between CSF 14-3-3 protein and sporadic CJD subtypes, distinguished by electrophoretic mobility of proteinase K-resistant prion protein (PrPSc) and genotype at codon 129 of the prion protein gene, has not been elucidated. Methods: The authors examined the 14-3-3 protein test in 90 patients with sporadic CJD. PrPSc type (type 1 or type 2) and the genotype at polymorphic codon 129 were determined in each patient. Mutations were excluded by prion gene sequencing. Results: The authors' findings indicate that the sensitivity of the 14-3-3 test is higher in patients with molecular features of the classic sporadic CJD than in patients with the nonclassic CJD subtypes. The difference appears to be related to the PrPSc type and not to the codon 129 genotype. Disease duration before 14-3-3 testing might also have an influence because it was shorter in classic sporadic CJD. Conclusion: The Creutzfeldt-Jakob disease clinical subtype should be considered when interpreting results of the 14-3-3 test.