We present the clinical and genetic characteristics of a Japanese patient with neuropathologically confirmed familial amyotrophic lateral sclerosis/parkinsonism dementia complex (ALS/PDC). The 68-year-old proband with an 8-year history of parkinsonism and neurogenic amyotrophy and her three siblings suffering from parkinsonism associated with dementia originated from the Kii Peninsula of Japan. The proband's brain exhibited mild frontal lobe atrophy, moderate atrophy of the pes hippocampi, decoloration of the substantia nigra and locus coerules, and atrophy of the anterior root of the spinal cord. Microscopic examinations revealed degeneration of the CA1 portion of the hippocampus to the parahippocampus gyrus, substantia nigra, locus coerules and the spinal anterior horn with Bunina bodies. Neurofibrillary tangles (NFTs) were observed in widespread regions of the central nervous system through the cerebral cortex to the spinal cord. The predominant distribution of NFTs in the the third layer of the cerebral cortex was compatible with the characteristic feature of ALS/PDC in Guam. No tau mutation was found in the proband. The lack of mutations in the tau gene not only in this patient but also in earlier reported cases of ALS in the Western Pacific seems to suggest that other genetic factors may be contributing to ALS/PDC.