Background and Aims Helicopter Emergency Medical Services (HEMS) for secondary transfer of stroke patients eligible for thrombectomy could have a significant impact on outcomes for patients residing in areas remote from a thrombectomy centre (TC). Remote units cannot sustain a 24/7 thrombectomy service locally and transfer to a TC is necessary. There are few data on cost-effectiveness of secondary transfer via HEMS to inform commissioning decisions. We are evaluating the cost-effectiveness of HEMS versus ground-based ambulance (GBA) for stroke thrombectomy in England. Method Using Geographic Information System data, we identified unavoidably remote hospitals serving a population of ≤800,000 (where initiating a local sustainable 24/7 thrombectomy service is not feasible) and >1 hour by GBA from the nearest designated TC. We previously estimated the proportion of CT/CTA-confirmed stroke patients admitted with NIHSS≥6 within 4.5 hours. Probability of receiving thrombectomy via HEMS or GBA was derived from average journey times. Quality Adjusted Life Years will be calculated for secondary transfer by HEMS and GBA to the most proximal TC to derive an incremental cost-effectiveness ratio. Results Annual stroke incidence of 3,860 at unavoidably remote hospitals (≥75km transfer distance), of which 508 patients would be transferred by HEMS. Ongoing survey of HEMS to establish operational parameters and costs to inform cost effectiveness model is ongoing and will be presented with the health economic data. Conclusion HEMS is an option for secondary transfer of patients eligible for thrombectomy from unavoidably “small” and remote hospitals. Estimates of HEMS cost-effectiveness will be presented to inform the optimal organisation of thrombectomy service delivery.