PURPOSE: The increasing burden of out-of-pocket expenses borne by older adults with frailty can be a considerable challenge in efforts toward improving societal health. This study estimated the cost of frailty for older adults by employing cost of illness theory. METHODS: Five electronic databases were searched (without any language or year restriction) for relevant articles from their inception to April 2024. Studies investigating the cost of frailty and prefrailty for older adults (aged ≥ 60 years) were included. RESULTS: A total of 51 studies were included. The findings revealed that frailty significantly increased mean total costs by US286 and US653 compared with the costs for individuals with prefrailty and robustness, respectively. The cost difference between the prefrailty and robust groups was US729. The increases in indirect costs did not significantly differ between the prefrailty and robust groups or between the frailty and robust groups. The total cost by setting was significantly increased in the frailty group relative to the prefrailty and robust groups. The results stratified by continent or region revealed that only the frailty and prefrailty groups in North America experienced significant increases in total costs relative to the robust group. However, in the Asia-Pacific region and Europe, no significant results were noted. CONCLUSIONS: This is the first meta-analysis to employ cost of illness theory to investigate the cost of frailty. Our findings can help providers of health-care services and professional workers develop effective and comprehensive intervention plans and services that can be provided for older adults with frailty.