We described recent knowledge and outline about a diagnosis and clinical typing of sporadic prion disease. Diagnostic procedure and classification based on a pattern of Western blotting of PrP(Sc), neuropathologic findings, and clinical features. In addition, we described a clinical significance of total tau protein, significance of a diffusion-weighted images of MRI. Analysis of 112 cases of sporadic prion diseases showed 92.3% at positive rate. Sensitivity and specificity were 95.5% and 95.7%, respectively by total tau protein assay of 44 cases of prion diseases.