The ethical pre-condition of randomised controlled trials is, at present, the presence of equipoise. This refers to an opinion of the investigator that there is uncertainty as to the merits of the treatments being compared. It is argued that since the decision to enrol is the potential subject's, the investigator's opinion is not ethically relevant. It is proposed instead that equipoise be patient-centred, and that a trial is in equipoise for a patient when enrolling gives them the same chance of a good outcome as not enrolling. It is shown that trial enrolment is normally easily the best strategy for achieving a good outcome, and that trials currently thought to be unethical may be in patient-centred equipoise. This is so for three reasons: (1) patients in trials receive superior care, (2) trial enrolment minimises the risk of being a victim of a therapeutic disaster and (3) health professionals make mistakes, and a 50% chance of receiving the worse treatment until a trial reports is always better than any chance of receiving the worse treatment indefinitely. It is concluded that so long as the standard of professional conduct is the furtherance of patients' objective interests randomised controlled trials are ethical.