Background: The loss of muscle mass, known as sarcopenia, is a natural process of aging that is associated with adverse health outcomes regardless of age. Because cancer is a disease of aging, interest in sarcopenia and its potential impact in multiple cancer populations has increased significantly. Bioelectrical impedance analysis (BIA) is a guideline-accepted method for sarcopenia detection. This systematic review assesses the literature pertaining to BIA use in the detection of sarcopenia in adults with cancer. Materials and Methods: In this systematic review, a search of the literature for randomized controlled trials and observational studies was conducted using MEDLINE, Cochrane CENTRAL, and EMBASE, through July 15, 2019. The study is registered at Prospero (CRD 42019130707). For study inclusion, patients had to be aged 18 years or older and diagnosed with solid or hematological neoplasia, and BIA had to be used to detect sarcopenia. Results: Through our search strategy, 5,045 articles were identified, of which 24 studies were selected for inclusion in the review (total number of 3,607 patients). In five studies, BIA was rated comparable to axial computed tomography (CT) scan, calf circumference, or grip strength for sarcopenia screening. In 14 studies, BIA-identified sarcopenia was associated with adverse clinical outcomes. Conclusion: BIA is an accurate method for detecting sarcopenia in adults with cancer prior to treatment and is a viable alternative to CT, dual-energy x-ray absorptiometry, and magnetic resonance imaging in oncology clinical practice. Implications for Practice: Bioelectrical impedance analysis (BIA) is an attractive method for identifying sarcopenic patients in clinical practice because it provides an affordable, noninvasive test that can be completed within a few minutes during a clinic visit. BIA does not require highly skilled personnel, and results are immediately available. This systematic review summarizes the literature pertaining to BIA assessment of sarcopenia in adults with cancer, with a focus on its use in diverse cancer populations.