‘Big data’ and data-intensive research approaches are rapidly gaining momentum in health and biomedical research, with potential to transform health at all levels from personal to public. The use of ‘big data’ for health research, however, raises a number of ethical challenges. In this paper I discuss ethical aspects of the advent of big data in health. I argue that although public discourse has focused on immediate concerns relating to use of individuals’ information, ‘big health data’ requires us to explore alternative conceptual approaches to research ethics, including the ‘social contract’ model. Further, we need to think beyond health research uses of data to the social consequences of big data epistemology and practice, and the moral implications of ‘datafying’ the human.