Last year Amazon captured 40% of online sales partly as a result of accurate personalized predictions designed to help consumers discover what they want using a machine learning algorithm. In health care, we aspire to the same goal: accurate personalized predictions, although in the healthcare arena we are interested in predicting outcomes of medical consequence to our patients rather than their next consumer whim. This revolution in predictive power has changed the nature of online buying, and now seems poised to transform medical practice. Our challenge is to ensure that this transition to personalized medicine is safely implemented. If risk prediction tools are to be used in clinical care, it is essential that they be vetted with the same care as any new drug or medical device.