Demência due to prion disease is a primary neurodegenerative disease caused by a group of spongiform encephalopathies resulting from abnormal prion protein accumulation in the brain. These can be sporadic, genetic (caused by mutations in the prion-protein gene), or transmissible (acquired from an infected individual). Onset is insidious and there is a rapid progression of symptoms and impairment characterised by cognitive deficits, ataxia, and motor symptoms (myoclonus, chorea, or dystonia). Diagnosis is typically made on the basis of brain imaging studies, presence of characteristic proteins in spinal fluid, EEG, or genetic testing.