Purpose <p>Frailty is common among older adults admitted to geriatric rehabilitation and influences outcomes such as recovery, length of stay, and discharge destination. Identifying reliable tools to assess frailty in this setting is essential for clinical decision-making. This review aims to identify the tools used to detect frailty in geriatric rehabilitation settings, analyze the associations between frailty and rehabilitation outcomes, and assess their ability to predict short- and long-term clinical outcomes in patients admitted to post-acute geriatric inpatient rehabilitation.</p> Method <p>A systematic review was conducted using Medline/PubMed and CINAHL databases. Studies were eligible if they focused on geriatric rehabilitation and analyzed associations between frailty and rehabilitation-sensitive outcomes.</p> Results <p>Twenty-five studies were included, covering a range of frailty instruments. Across studies, frailty consistently predicted mortality, institutionalization, functional recovery, and patient-reported outcomes. The Clinical Frailty Scale (CFS) and Frailty Index (FI) were the most frequently used and showed the most consistent associations with these outcomes, with reported AUC values typically between 0.60 and 0.73, and up to 0.82 for short-term mortality. Performance-based tools such as gait speed and the Frailty Phenotype were particularly predictive of functional outcomes.</p> Conclusion <p>The CFS and FI currently represent the most validated and feasible approaches for frailty assessment in geriatric rehabilitation, while direct head-to-head comparisons between tools remain limited. Detecting frailty at admission can help anticipate rehabilitation trajectories and guide individualized care strategies.</p>