We compared clinical data from two related Chinese patients with fatal familial insomnia (FFI) and collected information about their pedigree. The clinical features in the two cases were similar and included initial progressive insomnia and sympathetic activation, which persisted throughout the clinical course. A total of 135 members of this family, across seven generations, were retrospectively investigated. Eleven family members, including the two FFI cases, were found to have died with similar neurological problems. Analysis of PRNP in 32 family members revealed eleven carrying the D178N allele, including the two FFI patients. Spongiform degeneration in brains was not found, but gliosis was obvious in the thalamus of the two cases at postmortem. Proteinase K-resistant prion protein (PrP) was not found in proband's brain by immunohistochemistry, but observed in some areas of brain for both cases by PrP-specific Western blot. Investigation of the pedigree has led to the identification of an additional 9 family members who had similar clinical symptoms and 9 currently healthy individuals with the D178N mutation.