OBJECTIVES: Trials comparing the effects of transfusing RBC units of different storage durations have considered mortality or morbidity as outcomes. We perform the first economic evaluation alongside a full age of blood clinical trial with a large population assessing the impact of RBC storage duration on quality-of-life and costs in critically ill adults. DESIGN: Quality-of-life was measured at 6 months post randomization using the EuroQol 5-dimension 3-level instrument. The economic evaluation considers quality-adjusted life year and cost implications from randomization to 6 months. A generalized linear model was used to estimate incremental costs (2016 U.S. dollars) and quality-adjusted life years, respectively while adjusting for baseline characteristics. SETTING: Fifty-nine ICUs in five countries. PATIENTS: Adults with an anticipated ICU stay of at least 24 hours when the decision had been made to transfuse at least one RBC unit. INTERVENTIONS: Patients were randomized to receive either the freshest or oldest available compatible RBC units (standard practice) in the hospital transfusion service. MEASUREMENTS AND MAIN RESULTS: EuroQol 5-dimension 3-level utility scores were similar at 6 months-0.65 in the short-term and 0.63 in the long-term storage group (difference, 0.02; 95% CI, -0.00 to 0.04; p = 0.10). There were no significant differences in resource use between the two groups apart from 3.0 fewer hospital readmission days (95% CI, -5.3 to -0.8; p = 0.01) during follow-up in the short-term storage group. There were no significant differences in adjusted total costs or quality-adjusted life years between the short- and long-term storage groups (incremental costs, -$2,358; 95% CI, -$5,586 to $711) and incremental quality-adjusted life years: 0.003 quality-adjusted life years (95% CI, -0.003 to 0.008). CONCLUSIONS: Without considering the additional supply cost of implementing a freshest available RBC strategy for critical care patients, there is no evidence to suggest that the policy improves quality-of-life or reduces other costs compared with standard transfusion practice.