Simple SummaryCAR T therapies axicabtagene ciloleucel (axi-cel) and tisagenlecleucel (tisa-cel) have been approved in Spain for patients with relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL), given their favourable outcomes for overall survival and progression-free survival. However, the cost of these treatments must be weighed within the context of the Spanish health system. In this study, we assessed the cost-effectiveness and cost-utility of axi-cel vs. tisa-cel from the Spanish National Health System perspective. Using commonly applied willingness-to-pay thresholds in Spain, our analysis shows that axi-cel is highly cost-effective when compared to tisa-cel in R/R DLBCL. These results could be used to support decision-making criteria for axi-cel financing.The study aimed to assess the cost-effectiveness of axicabtagene ciloleucel (axi-cel) vs. tisagenlecleucel (tisa-cel) for the treatment of relapsed/refractory (R/R) diffuse large B-cell lymphoma (DLBCL) after ≥2 lines of systemic therapy in Spain. A lifetime partitioned survival mixture cure model, which comprises pre-progression, post-progression, and death health states, was used to estimate the accumulated costs and outcomes in terms of life years gained (LYG) and quality-adjusted life years (QALY). A matching-adjusted indirect comparison was used to reweight patient-level data from ZUMA-1, the pivotal clinical trial for axi-cel, to aggregate-level data from the pivotal tisa-cel trial, JULIET. The analysis was performed from the National Health System perspective, thus only direct costs were included. Sensitivity analyses (SA) were performed. Axi-cel yielded 2.74 incremental LYG and 2.31 additional QALY gained per patient compared to tisa-cel. Total incremental lifetime costs for axi-cel versus tisa-cel were €30,135/patient. The incremental cost-effectiveness ratio of axi-cel versus tisa-cel resulted in €10,999/LYG and the incremental cost-utility ratio in €13,049/QALY gained. SA proved robustness of the results. Considering the frequently assumed willingness-to-pay thresholds in Spain (€22,000/QALY and €60,000/QALY), axi-cel is a cost-effective treatment vs. tisa-cel for adult patients with R/R DLBCL in Spain.