This paper discusses some of the ethical and legal issues that the recommendations contained in the Cass Review raise. It focuses, in particular, on the recommendation that hormonal treatment in the form of puberty blockers be made available only within a clinical trial. This paper explains why a clinical trial is highly unlikely to expand the evidence base in the way stated in the Review, and that other kinds of research, such as observational and longitudinal studies, are much more likely to be useful in this context. Those other kinds of research, however, are considered by Cass to provide low quality of evidence. In addition to the feasibility of clinical trials in this context, there are important ethical issues, which relate to consent and its voluntariness.