Machine learning -- the use of computational algorithms to find patterns in data -- is increasingly being deployed in clinical contexts to support diagnosis and treatment decisions. In the context of growing volumes of clinical data available in electronic form, there is an opportunity to realise dramatic changes in the practice of medicine through the application of large-scale health data analytics and predictive modeling. This talk will introduce a vision for the use of data-driven methods in health, while also raising important questions about the implementation of this vision: is it conceivable that one day your doctor might be replaced by a digital system? What are the risks?