Humans are constantly being attacked by infectious agents. Although infectious diseases are conditions in-and-of themselves, they can accompany other disorders. In the 1990s several researchers raised the question of a link between infectious diseases and mental illness disorders to some unknown degree, asserting “a better understanding of the role of infection may speed treatment and prevention efforts and reduce the degree of disability and stigma associated with mental illness”. Others believe not only a link exists between mental illness and infectious disease but even where pathogenesis disregards the brain, a silent epidemic of mental illness often accompanies outbreaks of infectious diseases. This chapter discusses select infectious diseases in adults, and their causes and symptoms. It describes the significance of these diseases for adults with disabilities and implications for psychosocial adjustment, employment, and quality of life. Finally, it presents a glossary of terms to assist the reader.