Equipoise is advocated as a means of achieving high scientific and ethical standards in randomised trials. As used in the context of research the word describes a state of uncertainty characterised by the belief that in a trial no arm is known to offer greater harm or benefit than any other arm. Clinicians who lack personal equipoise are advised to accept clinical or communal equipoise, based on current unresolved disagreement among the medical profession. Equipoise is mainly discussed in the literature (...) as an issue for senior doctors and research directors. Limitations of professional equipoise are reviewed, and data on the neglected topic of patients' equipoise are reported using the example of breast cancer trials. In theory, a patient who gives informed and voluntary consent to enter a randomised trial has achieved the equilibrium of equipoise. In practice, equipoise among patients ranges from personal to proxy acceptance. (shrink)