Purpose Elderly trauma is increasing due to the ageing population. Studies including only major trauma or patients admitted under specialised trauma units exclude a large portion of elderly patients, as most elderly traumas are minor. Prior studies demonstrated that frailty surpasses injury severity score (ISS) to predict mortality. This study explored the association between clinical frailty score (CFS), age and ISS with in-hospital and 12-month mortality in an expanded cohort of elderly patients, including minor and major trauma, and admissions under all units at a trauma centre. Methods The study included all patients aged ≥65 years admitted following trauma to the Royal Melbourne Hospital, a Level 1 trauma centre, in 2022. The primary outcomes were in-hospital and 12-month post discharge mortality, with regression analysis to explore factors associated with mortality. Results 1381 patients were included. Increasing CFS increased in-hospital and 12-month post discharge mortality. Conversely, increasing ISS increased in-hospital but decreased 12-month post discharge mortality. Multivariate analysis for in-hospital mortality showed CFS and ISS were significant factors. For 12-month mortality, age, CFS and low fall were significant in multivariate regression. Conclusion CFS was associated with in-hospital and 12-month post discharge mortality, while ISS was only associated with in-hospital mortality. While this is not a new finding, this study is unique as it included a complete cohort of elderly patients admitted to hospital following trauma. The importance of frailty in predicting poor outcome cannot be understated. Ensuring frail patients are allocated the needed resources to mitigate poor outcomes is crucial.