OBJECTIVE: To characterize the distribution of tau pathology in patients with amyotrophic lateral sclerosis/parkinsonism-dementia complex on the Kii Peninsula (Kii ALS/PDC) by tau PET using [11C]PBB3 as ligand. METHODS: This is a cross-sectional study of five patients with ALS/PDC and one asymptomatic participant with a dense family history of ALS/PDC from the Kii Peninsula who took part in this study. All were men, and their age was 76 ± 8 (mean ± SD) years. Thirteen healthy men (69 ± 6 years) participated as healthy controls (HCs). Dynamic PET scans were performed following injection of [11C]PBB3, and parametric PET images were generated by voxel-by-voxel calculation of binding potential (BPND) using a multilinear reference tissue model. [11C]PiB PET, MRI, and cognitive tests were also performed. RESULTS: A voxel-based comparison of [11C]PBB3 BPND illustrated PET-detectable tau deposition in the cerebral cortex and white matter, and pontine basis including the corticospinal tract in Kii ALS/PDC patients compared with HCs (uncorrected p < 0.05). Group-wise VOI analysis of [11C]PBB3 BPND images showed increased BPND in the hippocampus and in frontal and parietal white matters of Kii ALS/PDC patients relative to HCs (p < 0.05, Holm-Sidak multiple comparisons test). BPND in frontal, temporal, and parietal gray matters correlated with Mini-Mental State Examination scores in Kii ALS/PDC subjects (p < 0.05). All Kii ALS/PDC patients were negative for [11C]PiB (amyloid β) except one with marginal positivity. CONCLUSION: [11C]PBB3 PET visualized the characteristic topography of tau pathology in Kii ALS/PDC, corresponding to clinical phenotypes of this disease.