INTRODUCTION: Functional deterioration preceding acute hospital admission may be associated with poorer in-hospital outcomes. We sought to investigate the association between functional decline in the month preceding admission and in-hospital outcomes. MATERIALS AND METHODS: Consecutive patients admitted under geriatric medicine over 5 years were prospectively included. Pre-hospital decline was defined as decrease in Modified Barthel Index (MBI) between pre-morbid status (1 month prior) and admission. The primary outcome was in-hospital functional decline (decline in MBI and/or new assistance/aid to mobilise). Secondary outcomes included length-of-stay (LOS; highest quartile), in-hospital falls and death. RESULTS: Amongst 1458 patients (mean age 82.0; 60.91% female), 76.89% (1121/1458) experienced pre-hospital MBI decline. On univariate logistic regression, pre-hospital MBI decline was associated with in-hospital functional decline (OR 15.83, p < 0.001). Adjusting for age, nursing home residence, pre-morbid MBI, in-hospital referral source, dementia, adverse drug reaction and number of active diagnoses, pre-hospital decline was independently associated with in-hospital functional decline (OR 15.22, CI 10.89-21.26, p < 0.001). On univariate analysis, those with pre-hospital decline had more in-hospital falls (OR 2. 91, p = 0.02). Adjusting for age, sex, dementia, number of active diagnoses, and ambulation, no strong association was observed between pre-hospital decline and in-hospital falls (OR 1.86, p = 0.08). Prolonged LOS ≥ 20 days was more common amongst patients with pre-hospital decline on univariate (OR 1.95, p < 0.001) but not adjusted analyses (p = 0.14). No association was observed with in-hospital death. CONCLUSION: Pre-hospital functional decline was associated with poorer in-hospital functional outcomes. Exploration of early interventions to optimise function in such patients is needed.