This article reviews research on the role of stress in infectious disease as measured either by illness behaviors (symptoms and use of health services) or by verified pathology. Substantial evidence was found for an association between stress and increased illness behavior, and less convincing but provocative evidence was found for a similar association between stress and infectious pathology. Introverts, isolates, and persons lacking social skills may also be at increased risk for both illness behaviors and pathology. Psychobiological models of how stress could influence the onset and progression of infectious disease and a psychological model of how stress could influence illness behaviors are proposed.