The presence of many neurofibrillary tangles (NFTs) in the central nervous system is a hallmark of amyotrophic lateral sclerosis (ALS) and parkinsonism-dementia complex (PDC) in people living in the Kii peninsula of Japan and in the island of Guam. To determine whether or not ALS and PDC are on a spectrum of a single tauopathy, we investigated the topography of NFTs semiquantitatively in two patients with ALS, three with PDC, and two with "PDC plus ALS" (PDC followed by ALS) on the basis of clinical symptoms. NFTs were counted under x100 magnification of Gallyas-Braak stained preparations and were plotted on brain maps of the hemisphere, brainstem, and the spinal cord. In all cases, the hippocampus, particularly in the CA1 field, the parahippocampal gyrus, amygdaloid nucleus, and the temporal poles were most severely affected. In the neocortex, layers II-III were more severely affected by NFTs than layers V-VI. In the spinal cord, a few NFTs were revealed in the intermediate gray. NFTs were dense in all cases of PDC and "PDC plus ALS" and variable in density in ALS cases, although the topography was similar between them. We conclude that similar topographical distribution of NFTs in ALS and PDC in people living in the Kii peninsula of Japan suggests a single tauopathy.