According to the recently established molecular basis for phenotypic heterogeneity of sporadic Creutzfeldt-Jakob disease (CJD), six different phenotypes are characterized by the size of the protease-resistant fragment of the pathological prion protein (types 1 and 2) and homozygosity or heterozygosity for methionine or valine at codon 129 of the prion protein gene (designated by MM1, MM2, MV1, MV2, W1, and W2). In the present investigation, we analyzed the value of commonly used clinical tests (electroencephalogram [EEG], detection of 14-3-3 protein in cerebrospinal fluid [CSF], and hyperintensity of the basal ganglia in magnetic resonance imaging) for the clinical diagnosis in each CJD phenotype. The detection of periodic sharp and slow wave complexes in the EEG is reliable in the clinical diagnosis of MM1 and MV1 patients only. The CSF analysis for 14-3-3 protein showed high sensitivity in all analyzed subgroups with the exception of MV2 patients. Valine-homozygous patients had a negative EEG, but most had detectable levels of neuronal proteins in the CSF. The sensitivity of the magnetic resonance imaging was 70%, irrespective of the subgroup, but was particularly reliable in the clinical diagnosis of MV2 patients. The widening spectrum of diagnostic techniques in CJD is not only useful in the increased accuracy of the clinical diagnosis but should also lead to the identification of more atypical cases of sporadic CJD.