OBJECTIVES: Acute graft versus host disease is a complication of bone marrow transplants in which T cells from the donor graft attack the hosts tissues. Treatment cost is often used as a determinant of treatment choice, but little economic data exists to inform decisions. Non-responders to treatment are less likely to survive but less likely to incur expensive treatment costs, making it challenging to identify appropriate economic endpoints. At a single institution, we tested the feasibility of an economic approach to measure the value of photopheresis as a combined agent, when compared to immunosuppression alone. The measures of value included net hospital costs and productivity. METHODS: We examined the records of all patients with severe aGvHD who met published eligibility criteria for photopheresis in the year before the service commenced and during the year after. Resource utilisation was based on number of days in hospital and administration of high cost drugs for GvHD and related complications. Relevance was determined by expert review. Costs were identified using the local pharmacy database and the unit reference costs database. RESULTS: This audit included 9 patients in the study arm and 7 patients in the comparison arm. The mean reduction in hospitalisation days per patient was 21.3% (74.7-58.7) and spend on high cost drugs per patient was reduced by 48.3% (£28,420-£14,688). The mean net reduction in costs per patient, adjusted for photopheresis treatment costs, was £28,040. Furthermore, all patients died in the comparator arm during the audit period, compared to 10% in the study group. CONCLUSIONS: The additional costs of treating non responders and treatment complications should be considered alongside direct therapy costs. The results of this audit may support the feasibility of economic studies to evaluate the cost effectiveness of treatments for rare life threatening diseases.