This systematic review synthesizes observational studies on the relationship between ageism and health. We searched 10 electronic databases and included 67 articles. The operationalization of ageism in these studies can be classified into three constructs: age stereotype, self-perceptions of aging, and age discrimination. Most ageism measures were used within a single study, and many lacked information about psychometric properties. Seven health domains-disease, mortality, physical/functional health, mental health, cognitive function, quality of life, and health behavior-have been used as outcomes. Evidence supports a significant association between ageism and health, particularly between self-perceptions of aging and health. Nine studies report moderators, which helps to identify those more vulnerable to negative effects of ageism and inform the development of interventions. The review suggests that the literature has examined limited dimensions of ageism, and that developing valid and reliable instruments for ageism-related concepts is a priority.