Alzheimer's disease (AD) is currently one of the most studied neurodegenerative disorders in humans. First reported in 1907, the disease has a familial form which represents approximately 5% of cases, while the remaining, sporadic cases are of multifactorial etiology. The disease progression of the latter form has specific pathological and functional characteristics, which have unknown etiology. Several authors have proposed a viral etiology for AD, while others implicate many neurotropic infectious agents. This review compares research findings regarding pathways and effects of neuropathological viruses with the pathways and effects involved in the progression of AD. The similarities are striking and provide a compelling argument for a pathogen-based etiology of AD.