Background. The prevalence of adults with Alzheimer disease (AD) aged >65 years is increasing and estimated to quadruple by 2051. Purpose. The aim of this study was to investigate postural stability in people with mild to moderate AD and factors contributing to postural instability compared with healthy peers (controls). Data Sources. A computerized systematic search of databases and a hand search of reference lists for articles published from 1984 onward (English-language articles only) were conducted on June 2, 2015, using the main key words “postural stability” and “Alzheimer’s disease.” Study Selection. Sixty-seven studies were assessed for eligibility (a confirmed diagnosis of AD, comparison of measured postural stability between participants with AD and controls, measured factors potentially contributing to postural instability). Data Extraction. Data were extracted, and Downs and Black criteria were applied to evaluate study quality. Data Synthesis. Eighteen articles were analyzed using qualitative synthesis and reported based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Strength of evidence was guided by the Grading of Recommendations Assessment, Development and Evaluation. Strong evidence was found that: (1) older adults with mild to moderate AD have reduced static and functional postural stability compared with healthy peers (controls) and (2) attentional demand during dual-task activity and loss of visual input were key factors contributing to postural instability. Limitations. Meta-analysis was not possible due to heterogeneity of the data. Conclusions. Postural stability is impaired in older adults with mild to moderate AD. Decreasing visual input and concentrating on multiple tasks decrease postural stability. To reduce falls risk, more research discerning appropriate strategies for the early identification of impairment of postural stability is needed. Standardization of population description and consensus on outcome measures and the variables used to measure postural instability and its contributing factors are necessary to ensure meaningful synthesis of data.