The first thing most of us think of when a patient presents with rapidly progressive dementia (RPD) is Creutzfeld-Jakob disease (CJD). But not so fast! Michael Geschwind, with Aissa Haman and Bruce Miller, of theUniversityofCaliforniaatSan Franciscowrote a good review article in Neurologic Clinics [Neurol Clin 25(2007) 783-807] entitled “Rapidly Progressive Dementia”. The authors reviewed the records of 825 patients referred to their institution for RPD, many with a presumptive diagnosis of CJD. Most of the patients ended up with the diagnosis of definite or likely prion disease. But 18% had other diseases, many of which were treatable. The non-prion causes of RPD, in descending order of incidence, included neurodegenerative, autoimmune, other infectious, psychiatric, and miscellaneous disorders. The most common neurodegenerative disorder presenting with RPD appears to be Alzheimer disease, particularly when present in conjunction with amyloid angiopathy.