OBJECTIVES: The objective was to evaluate the cost effectiveness of caplacizumab for the treatment of patients with acquired immune thrombocytopenic thrombotic purpura (iTTP) compared to standard of care from the perspective of the Brazilian Unified Health System (SUS). METHODS: A decision tree followed by a Markov model with a lifetime horizon was developed. Patients entered the model with an acute iTTP event. All patients were assumed to be admitted to hospital where they either respond to treatment or die. The model offered three health states: remission, relapse or death. Input data were obtained from literature searches with the data on efficacy of caplacizumab based on the HERCULES trial. The incremental cost-effectiveness ratio (ICER) was compared to the willingness-to-pay threshold for rare diseases of Brazilian reais (R$)120,000/quality-adjusted life years (QALYs). In addition to various sensitivity analyses, a value of information (VOI) analysis was conducted. RESULTS: In the base case, caplacizumab resulted in 0.70 QALYs gained, and cost R$1,333,601 more, with an ICER of R$1,901,729/QALY. The cost of the caplacizumab vial was the most influential parameter. Probabilistic analysis showed that caplacizumab was not cost effective in any iterations for the threshold of the rare disease. The expected value of perfect information per year is R$0. CONCLUSION: Although caplacizumab results in incremental QALYs, based on the proposed cost, caplacizumab is not cost effective from the SUS perspective, and VOI results indicate that further research would not be worthwhile.