Purpose: There is conflicting evidence on the effect of red blood cells (RBC) storage duration and clinical outcomes. We aimed to investigate the association between RBC storage duration and clinical outcomes in patients admitted to the intensive care unit (ICU). Materials and Methods: We retrospectively (2001-2011) studied adults admitted to the ICUs of 2 hospitals who received RBC. Using the mean, maximum and minimum age of RBC units transfused, we evaluated the association between RBC storage duration and mortality. We also analyzed the association between mean age of RBC units and length of stay (LOS) in survivors. We performed sensitivity analyses in patients who only received RBC in ICU and who only received leukodepleted RBC. Results: We studied 8416 patients who received a median of 4 (interquartile range, 2-7) RBC units. After multivariate analysis, age of RBC was not independently associated with mortality, including in the subgroup analyses. Furthermore, there was no clinically relevant relationship between mean RBC age and LOS. Conclusions: RBC storage duration was not associated with increased mortality nor ICU and hospital LOS. These results support the view that the effect of RBC storage duration on outcomes in critically ill patients is uncertain.