Public disclosure of the comparative performance of health care providers has been proposed as one mechanism of improving the quality of care. Performance data have been made public in the USA for over a decade and the provision of comparative information about quality of care is a central feature of current UK government health policy. The balance between the advantages and risks of pursuing such a policy in publicly funded health service is largely unknown. Advocates of public disclosure cite the role that comparative data can play in ensuring accountability, shifting the ownership of information (and therefore power) from professionals to service users and encouraging improvements in the processes and outcomes of care. However, these expectations are not necessarily realistic. There is some evidence that the public make little use of comparative data and there is a risk that public release may result in a loss of confidence in the health system and demoralisation of health service staff. In addition, there is a legitimate doubt that any early impact of disclosure will not be sustained and that the outcomes will not justify the necessary expenditure. In conclusion, we suggest that the theoretical benefits of promoting public disclosure as voiced by advocates of the policy may not be realised in practice.