Randomised clinical trials in surgery are relatively rare. There are many problems associated with the comparison of two types of surgical treatment. Comparison of surgical treatment and a non-operative approach is difficult because patient and surgeon are not blinded. In a recent study, the outcomes after arthroscopic lavage or debridement were no better than those after a placebo arthroscopic procedure. This placebo treatment appears ethically justified, because the risks to participants of this study were limited. Placebo surgery may help to resolve longstanding debates about several surgical procedures.