To determine whether changes in class I HDAC levels detected with [11C]Martinostat in DLB and PD participants were evident in postmortem brain tissue, we evaluated class I HDACs (HDAC1, HDAC2, and HDAC3) in anterior cingulate, inferior parietal cortex, and precentral gyrus tissue samples from DLB and PD patients and healthy controls (HC) without a premortem diagnosis of neurodegenerative disease. Here, HDAC9 is linked to Lewy body dementia.