Highlights • Non-surviving showed higher RDW than surviving patients. • There is an association between RDW and mortality. • RDW could be used as mortality biomarker. Purpose We have previously reported an association between high red blood cell distribution width (RDW) and mortality in septic and brain infarction patients. However, no association between RDW and mortality in coronavirus disease 2019 (COVID-19) patients has been reported so far; thus, the objective of this study was to determine if that association exists. Methods Prospective and observational study carried out in 8 Intensive Care Units from 6 hospitals of Canary Islands (Spain) including COVID-19 patients. We recorded RDW at ICU admission and 30-day survival. Results We found that patients who did not survive (n = 25) compared to surviving patients (n = 118) were older (p = 0.004), showed higher RDW (p = 0.001), urea (p