> The far wider relevance of prion mechanisms was first exemplified with the discovery of yeast prions but has also widened considerably with the recognition that the more common human neurodegenerative diseases, including Alzheimer’s and Parkinson’s diseases, involve accumulation and spread of assemblies of misfolded host proteins in what is often described as a ‘prion-like’ fashion with experimental transmission of relevant pathology in primates or mouse models. However, the importance for human disease was unclear until the recognition of human transmission of amyloid-beta (Aβ) pathology via iatrogenic routes after prolonged incubation periods, causing iatrogenic cerebral amyloid angiopathy (CAA) and raising the possibility that iatrogenic Alzheimer’s disease may occur at even longer latency.