Cerebrospinal fluid (CSF) amyloid-beta 1-42 (Aβ1-42) and amyloid positron emission tomography (PET) are the 2 main Alzheimer disease amyloid biomarkers that have been validated in neuropathologically confirmed Alzheimer disease cases. Although many studies have shown concordance of amyloid positivity or negativity between CSF Aβ1-42 and amyloid PET, several studies also reported discrepancies between these 2 Aβ biomarkers. We conducted a comparison of CSF Aβ1-42 level, amyloid PET, and autopsy findings in a case with progressive supranuclear palsy in which biomarker acquisition and postmortem pathologic examination were conducted almost at the same time. Our case with antemortem CSF Aβ1-42 (+)/amyloid PET (-) who was pathologically confirmed with Aβ pathology in the cerebral cortex may indicate CSF Aβ1-42 is more sensitive for assessing in vivo Aβ than amyloid PET.