OBJECTIVES:   Clinical trials have shown that transcatheter aortic valve implantation (TAVI) is an efficacious treatment option in patients with Severe Aortic Stenosis (SAS). This study aimed to assess the cost-effectiveness of TAVI compared with standard medical therapy (SMT) in inoperable patients with SAS, from the UK National Health Service (NHS) perspective. METHODS:   A novel 9 health state Markov model, with monthly cycles, to simulate the clinical course of inoperable patients with SAS treated with TAVI or SMT, was developed using MS Excel. Health states were based on heart failure severity defined by the New York Heart Association (NYHA) classification and the history of stroke. The analysis accounts for direct costs (NHS perspective) only and the time horizon was set at 10 years which can be considered lifelong in these patients. Clinical data on the patient’s progression over time by NYHA class and event rates were taken from the PARTNER 1B-trial. Costs and utilities were health state and event specific and retrieved from literature. Annual discounting of 3.5% was applied. The outcome of the analysis was cost (£) per quality adjusted life year (QALY) gained. The analysis included one way and probabilistic sensitivity analyses to investigate the impact of parameter variability on model outputs. RESULTS:   Compared with SMT, TAVI was associated with higher costs (£10,422) and more QALYs (0.711), resulting in an incremental cost-effectiveness ratio of £14,668. Sensitivity analyses indicated that the key drivers of the model were cost of TAVI, cost of balloon valvuloplasty and mortality. The probability of TAVI to be cost-effective using a willingness to pay threshold of £20,000/QALY versus SMT was 72%. CONCLUSIONS:   In the UK setting, TAVI can be considered a cost-effective treatment option versus SMT in inoperable patients with SAS.