It is widely recognized that older persons, especially those who have complex multimorbidity and/or cognitive impairment, are underrepresented in published clinical research. Yet, as we move into a silver era, with increasing numbers of older persons, we need to be adequately informed as regards trajectories and outcomes for older persons presenting to acute care. This will facilitate risk stratification, resource allocation, and service planning. Although randomized trials might be ideal, these can be costly, challenging, and time-consuming to conduct. By harnessing data that are collected in the course of everyday clinical care, we can build an evidence base comprised of real-world clinical data and which is inclusive, rather than exclusive, of older persons, including those with frailty, multimorbidity, and/or cognitive impairment and including those from culturally and linguistically diverse (CALD) backgrounds. In this context, we sought to investigate the association between functional decline in the month preceding admission and in-hospital outcomes. We prospectively included consecutive patients admitted under geriatric medicine over a 5-year period. We found that, among the 1,458 included patients (mean age of 82 years, 36% with a background history of dementia, 17% from a permanent residential facility [nursing home]), prehospital functional decline was associated with poorer in-hospital functional outcomes. Notably, prehospital decline maintained an independent association with in-hospital functional decline on multivariate analysis (adjusted odds ratio [aOR] = 15.22, confidence interval [CI] = [10.89–21.26], p < .001), after adjusting for age, nursing home residence, premorbid function, in-hospital referral source (in-hospital consult and transfer of care vs. other referral source), dementia, adverse drug reaction, and number of active diagnoses.