Originally described by Lugaresi et al. in 1986 (ref. 1), fatal familial insomnia (FFI) is a rare inherited neurological disease characterized by the subacute progression of intractable insomnia and other autonomic abnormalities, cerebellar and pyramidal signs, myoclonus and dementia; neuropathologically, the major feature is severe neuronal loss with associated gliosis in the ventral and mediodorsal thalamic nuclei. The disease has been related to the group of spongiform encephalopathies by virtue of the presence of low levels of proteinase-resistant amyloid protein (PrPres) in the brain, and of a pathogenic single-allele mutation at codon 178 of the PRNP gene that encodes PrPres (refs 2, 5). Here we report the successful transmission of the disease to experimental animals, placing FFI within the group of infectious cerebral amyloidoses.