BACKGROUND: The COVID-19 pandemic represents one of the greatest ever challenges for healthcare. In the UK and beyond, acute medical units (AMUs) are the first point of assessment and care for the majority of medical inpatients. By their design and systems, they inevitably played an important role in the COVID-19 response but to date little has been published on how the COVID-19 pandemic has affected how AMUs have reorganised their resources, processes and structure. METHODS: This retrospective study in August 2020 of 10 AMUs across Europe and Australasia used a standardised questionnaire to investigate existing practice and structure of AMUs, the national context of local hospital experience, changes to practice during the COVID-19 pandemic and views regarding future practice. RESULTS: Changes to AMU structure, process and organisation are described in two contexts: preventing and controlling the spread of COVID-19 and adding value to the patient's acute care journey in the local context. We describe novel practices that have arisen and highlight areas of concern. CONCLUSIONS: The AMUs were able to adapt to meet the demands of acute care delivery during the first wave of the COVID-19 pandemic. Operational planning and prioritisation of resources must be optimised to ensure sustainability of these services for future waves.