The process of leaving the European Union (EU) will have profound consequences for health and the National Health Service (NHS) in the UK. In this paper, we use the WHO health system building blocks framework to assess the likely effects of three scenarios we term soft Brexit, hard Brexit, and failed Brexit. We conclude that each scenario poses substantial threats. The workforce of the NHS is heavily reliant on EU staff. Financing of health care for UK citizens in the EU and vice versa is threatened, as is access to some capital funds, while Brexit threatens overall economic performance. Access to pharmaceuticals, technology, blood, and organs for transplant is jeopardised. Information used for international comparisons is threatened, as is...