BACKGROUND: In a context of overwhelming demand, mass transfers between intensive care units (ICU) were organized in France during the first COVID-19 epidemic wave (spring 2020). According to early reports, transferred patients experienced a 3-to-4-fold lower ICU case fatality. It is not known whether this difference stems only from the selection of healthier patients for transfer. RESEARCH QUESTION: Is the 28-day ICU case fatality of transferred patients different from that of matched control (not transferred) patients? STUDY DESIGN AND METHODS: Multicenter retrospective cohort study that included 285 transferred patients, and 667 control (not transferred) patients admitted simultaneously (± 2 days) to the same "origin" ICU and alive five days after the transfer date. The 28-day ICU case fatality and clinical events during ICU stay were compared in transferred and control patients. RESULTS: At ICU admission, age, COVID-19 severity, comorbidities and Simplified Acute Physiology Score II (SAPS II) were similar, but transferred patients were lighter (81 versus 89 kg, p