Three brothers in a family with Val30Met transthyretin (TTR) amyloid polyneuropathy (FAP) in Iiyama, Japan were studied pathologically. In this family, affected members have been reported to show typical clinical features of FAP, and some have been documented to exhibit symptoms and signs of central nervous system (CNS) involvement consisting of cerebellar ataxia and pyramidal tract signs. After the original description, this family was regarded as a unique phenotype of this form of FAP; however, subsequent molecular genetic studies revealed that some patients and asymptomatic members in the family had Val30Met TTR and/or spinocerebellar ataxia type 1 (SCA1) gene mutations. In this study, pathological examination of two patients with both FAP and CNS symptoms showed (1) TTR-immunoreactive leptomeningeal and cerebrovascular amyloid deposition compatible with Val30Met TTR FAP, and (2) neuronal loss and gliosis mainly in the Purkinje cell layer, spinocerebellar system, olivo-ponto-cerebellar system, dentato-rubral system, gracile nuclei, cuneate nuclei, and various nuclei of cranial nerves, accompanied by anti-expanded polyglutamine tract antibody positive neuronal intranuclear inclusions, all of which were compatible with the pathological findings of SCA1. On the other hand, the remaining patient with FAP symptoms only showed the former pathological finding alone. The present study demonstrates, at the pathological level, that Val30Met TTR FAP and SCA1 coexist in the same family members, and that the CNS dysfunction seen in the patients in this family is ascribable to SCA1 pathology but not to CNS amyloidosis.