This article presents the results of a study into the knowledge of doctors regarding three kinds medical treatment regulation at the end of life, the so-called KOPPEL study. One of the findings of this study is that most doctors know the law that regulates ending life at request (euthanasia) and guideline for palliative sedation quite well. However, hardly any of them know Book 7, Section 450.3 of the Dutch Civil Code, the section that regulates written treatment refusals. Apart from the description of the findings, we elaborate on three reasons that Aubert distinguishes for knowledge of the law: the period the regulation exists, the congruence between habits and norms of the law, and experience with the law. We conclude that Aubert’s factors do indeed explain the differences in knowledge of the doctors. In the discussion we come to the conclusion that sociology of law should not only pay attention to ‘what knowledge of the law is’ (Griffiths, Van Tol) and ‘which factors influence this knowledge’ (Aubert) but also to ‘how knowledge of law can be ascertained’. In our opinion the idea of scripts, as introduced by Schank and Abelson, can be of great help in this respect.