ABSTRACTBackgroundthere are around 100,000 new stroke cases and over a million people living with its consequences annually in the UK. This has large impacts on health and social care, unpaid carers and lost productivity. We aimed to estimate associated costs.Methodswe estimated 2014/2015 annual mean cost per person and aggregate UK cost of stroke for individuals aged ≥40 from a societal perspective. Health and social care costs in the first and subsequent years after stroke were estimated from discrete event simulation modelling, with probability of progression and length of receipt of different health and social care services obtained from routine registry and audit data. Unpaid care hours and lost productivity were obtained from trial data. UK unit costs were applied to estimate mean costs. Epidemiological estimates of stroke incidence and prevalence were then applied to estimate aggregate costs for the UK.Resultsmean cost of new-onset stroke is £45,409 (95% CI 42,054-48,763) in the first year after stroke and £24,778 (20,234–29,322) in subsequent years. Aggregate societal cost of stroke is £26 billion per year, including £8.6 billion for NHS and social care. The largest component of total cost was unpaid care (61%) and, given high survival, £20.6 billion related to ongoing care.Conclusionthe estimated aggregate cost of stroke substantially exceeds previous UK estimates. Since most of the cost is attributed to unpaid care, interventions aimed at rehabilitation and reducing new and recurrent stroke are likely to yield substantial benefits to carers and cost savings to society.