PURPOSE: Compare service delivery and clinical outcomes in Acute Geriatric Units (AGUs) between the United Kingdom and Spain. METHODS: Prospective observational study of consecutive patients admitted to AGU in two English and four Spanish hospitals 15th September to 15th November 2022. RESULTS: 650 patients (476 from SP and 174 from the UK) with an average age of 85.4 years in Spanish hospitals and 83.5 years in British hospitals. Similar frailty prevalence (73.1% Spain, 77.7% UK) but differences in medication, pressure ulcers, antipsychotic use, and therapy evaluations. Spain had shorter average stay (8.3 days) and higher mortality (14% vs 7.6% UK). No significant differences in advance care planning. CONCLUSIONS: UK patients were younger, more independent, with fewer health issues. UK hospitals provided more therapy, fewer antipsychotics, and lower mortality despite longer stays. Calls for further research, including cost-effectiveness analysis and long-term studies.