Over the past decades, randomised controlled trials (RCTs) have prevailed over clinical judgement, case reports, and observational studies and became the gold evidential standard in medicine. Furthermore, during the same time frame, RCTs became a crucial part of the regulatory process whereby a new therapeutic can gain access to the drug market. Today, clinical trials are large and tightly regulated enterprises that have to comply with ethical requirements while maintaining high epistemic standards, a balance that becomes increasingly difficult as the research questions become more sophisticated. In this review, the author will discuss some of the most important ethical issues surrounding RCTs, with an eye to the most recent debates and the context of oncological research in particular.