BACKGROUND: The Movement Disorder Society criteria for progressive supranuclear palsy introduced the category "probable 4-repeat (4R)-tauopathy" for joint clinical diagnosis of progressive supranuclear palsy and corticobasal degeneration. OBJECTIVES: To validate the accuracy of these clinical criteria for "probable 4R-tauopathy" to predict underlying 4R-tauopathy pathology. METHODS: Diagnostic accuracy for 4R-tauopathies according to the established criteria was estimated retrospectively in autopsy-confirmed patients with progressive supranuclear palsy and corticobasal degeneration (grouped as 4R-tauopathies), and Parkinson's disease, multiple system atrophy, and frontotemporal lobar degeneration (grouped as non-4R-tauopathies). RESULTS: We identified 250 cases with progressive supranuclear palsy (N = 195) and corticobasal degeneration (N = 55) and with and non-4R-tauopathies (N = 161). Sensitivity and specificity of "probable 4R-tauopathy" was 10% and 99% in the first year and 59% and 88% at final record. CONCLUSIONS: The new diagnostic category "probable 4R-tauopathy" showed high specificity and may be suitable for the recruitment of patients with progressive supranuclear palsy and corticobasal degeneration into therapeutic trials targeting 4R-tauopathy. The low sensitivity underpins the need for diagnostic biomarkers. © 2019 International Parkinson and Movement Disorder Society.