Use of a placebo control in surgical trials is a divisive issue. We argue that, in principle, placebo controls for surgery are necessary in the same way as for medicine. However, there are important differences between these types of trial, which both increase justification and limit application of surgical studies. We propose that surgical randomised placebo-controlled trials are ethical if certain conditions are fulfilled: the presence of equipoise, defined as a lack of unbiased evidence for efficacy of an intervention; clinically (...) important research question; the risk to patients is minimised and reasonable; there is uncertainty about treatment allocation rather than deception; there is preliminary evidence for efficacy, which justifies a placebo-controlled design; and ideally, the placebo procedure should have some direct benefit to the patient, for example, as a diagnostic tool. Placebo-controlled trials in surgery will most often be justified when surgery is performed to improve function or relieve symptoms and when objective outcomes are not available, while the risk of mortality or significant morbidity is low. In line with medical placebo-controlled trials, the surgical trial should be sufficiently powered and standardised so that its results are valid, consent should be valid, the standard treatment or rescue medication should be provided if possible, and after the trial, the patients should be told which treatment they received and there should be provision for post-trial care if the study may result in long-term negative effects. We comment and contrast our guidelines with those of the American Medical Association. (shrink)