There can be little doubt, at least in the Western world, that autonomy is the ruling principle in contemporary bioethics. In spite of its ‘triumph’ however, the dominance of the utilitarian concept of autonomy is being increasingly questioned. In this paper, I explore the nature of autonomy, how it came to displace the Hippocratic tradition in medicine and how different concepts of autonomy have evolved. I argue that the reduction of autonomy to ‘the exercise of personal choice’ in medicine has led to a ‘tyranny of autonomy’ which can be inimical to ethical medical practice rather than conducive to it. I take the case of Kerrie Wooltorton as an illustration of how misplaced adherence to respect for patient autonomy can lead to tragic consequences. An analysis of autonomy based on the work of Rachel Haliburton is described and applied to the role of autonomy in a recent bioethical debate — that arising from Savulescu's proposal that conscientious objection by health-care professionals should not be permit..