The mechanisms underlying Alzheimer's disease and Lewy body disease have long been a controversial subject among neurologists and neuropathologists. Here, we hypothesize that three most common histopathological structures, Lewy body (LB), neurofibrillary tangle (NFT) and neuritic senile plaque (NP) found in neurodegenerative diseases are different stages of the same lesion. Lewy body disease (LBD) and Alzheimer's disease (AD) are based on a similar or the same pathogenic mechanism. Different clinical manifestations and pathological features found in postmortem brains between LBD and AD is due to the different intensities of initial insults, rate of the disease progression and temporal involvement of different brain regions during the AD development.