The neuropathologic examination is considered to provide the gold standard for Alzheimer disease (AD). To determine the accuracy of currently used clinical diagnostic methods, clinical and neuropathologic data from the National Alzheimer's Coordinating Center, which gathers information from the network of National Institute on Aging (NIA)-sponsored Alzheimer Disease Centers (ADCs), were collected as part of the National Alzheimer's Coordinating Center Uniform Data Set (UDS) between 2005 and 2010. A database search initially included all 1198 subjects with at least one UDS clinical assessment and who had died and been autopsied; 279 were excluded as being not demented or because critical data fields were missing. The final subject number was 919. Sensitivity and specificity were determined based on "probable" and "possible" AD levels of clinical confidence and 4 levels of neuropathologic confidence based on varying neuritic plaque densities and Braak neurofibrillary stages. Sensitivity ranged from 70.9% to 87.3%; specificity ranged from 44.3% to 70.8%. Sensitivity was generally increased with more permissive clinical criteria and specificity was increased with more restrictive criteria, whereas the opposite was true for neuropathologic criteria. When a clinical diagnosis was not confirmed by minimum levels of AD histopathology, the most frequent primary neuropathologic diagnoses were tangle-only dementia or argyrophilic grain disease, frontotemporal lobar degeneration, cerebrovascular disease, Lewy body disease and hippocampal sclerosis. When dementia was not clinically diagnosed as AD, 39% of these cases met or exceeded minimum threshold levels of AD histopathology. Neurologists of the NIA-ADCs had higher predictive accuracy when they diagnosed AD in subjects with dementia than when they diagnosed dementing diseases other than AD. The misdiagnosis rate should be considered when estimating subject numbers for AD studies, including clinical trials and epidemiologic studies.