The 'informed consent' process has been placed at the centre of bioethical and policy discourses about how the autonomy and rights of patients can best be protected. Although there has been critical analysis of how the process functions in relation to participation in research and particular ethical 'dilemmas', there has been little examination of the routine business of consenting to medical procedures. Evidence is now beginning to emerge that people may consent to surgery even when reluctant to do so. In this paper, we develop an analysis informed by Bourdieusian and interactionist social theory of the accounts of 25 British women who consented to surgery in obstetrics and gynaecology. Of these, nine were ambivalent or opposed to having an operation. When faced with a consent form, women's accounts suggest that they rarely do anything other than obey professionals' requests for a signature. Women's capacity to act is reduced as they become enmeshed in the hospital structure of tacit, socially imposed rules of conduct. However, the interactionist account of power operating through the social rules of particular situated encounters, and the sanctions associated with rule-breaking, may not provide a sufficiently powerful explanation for why women submit to surgery they are opposed or ambivalent towards. Bourdieu's concepts of habitus, capital and symbolic power/violence offer a potentially more elaborated account, by showing how the practical logic that women apply in the field of surgery confers a 'sense of place' relative to professionals. Women experience deficits in capital, intensified by their physical vulnerability in critical situations, that severely constrain their ability to exercise choice. This work demonstrates the weakness of the consent process as a safeguard of autonomy. Far from reinforcing autonomy, the process may reinforce rather than disrupt passivity, but more generally our findings raise the question of the extent to which autonomy is an illusory goal.