Assessing sarcopenia, the age-related loss of muscle mass and function, in institutionalized older adults is a challenging task. Data on its prevalence in residential facilities are scant and highly variable. Our objective was to report the prevalence of sarcopenia in older adults living in residential facilities (nursing/long term-care homes and assisted-living facilities) and review the criteria and methodologies used to diagnose sarcopenia in this setting. Bibliographic searches were carried out in 6 electronic databases (Medline via PubMed, Web of Science, Scopus, CINAHL, LILACS, and Cochrane) with the use of the Medical Subject Heading terms "Sarcopenia" and "Residential Facilities." We included studies that evaluated the prevalence of sarcopenia among older adults (aged ≥60 y) living in residential facilities. Forty-four studies were identified, of which 21 studies were included after applying eligibility criteria. The reported prevalence of sarcopenia ranged widely between 17.7% and 73.3% in long term-care homes and between 22% and 87% in assisted-living facilities. Most studies (n = 14) followed the consensus on sarcopenia diagnosis published by the European Working Group on Sarcopenia in Older People. In the other 7 studies, sarcopenia was diagnosed according to muscle mass, which was measured via 5 different techniques, most frequently bioelectrical impedance analysis, establishing cutoff scores for low muscle mass with the use of 5 different indexes, most frequently the skeletal muscle index. There are major differences in study design, methodology, and the approach to sarcopenia diagnosis in this setting, which would, in part, explain the enormous variability in the reported prevalence data. The lack of consensus on the correct diagnostic approach hampers the implementation of appropriate nutritional interventions.