Prisoner health is influenced as much by structural determinants (institutional, environmental, political, economic and social) as it is by physical and mental constitutions of prisoners themselves. Prison health may therefore be better understood with greater insight into how people respond to imprisonment - the psychological pressures of incarceration, the social world of prison, being dislocated from society, and the impact of the institution itself with its regime and architecture. As agencies of disempowerment and deprivation, prisons epitomise the antithesis of a healthy setting. The World Health Organisation's notion of a 'healthy prison' is in this sense an oxymoron, yet the UK government has signalled that it is committed to WHO's core health promotion principles as a route to reducing health inequalities. This paper reports on the findings of an ethnographic study which was conducted in an adult male training prison in England, using participant observation, group interviewing, and one-to-one semi-structured interviews with prisoners and prison officers. The paper explores how different layers of prison life impact on the health of prisoners, arguing that health inequalities are enmeshed within the workings of the prison system itself.