In recent years, a commitment to professional ethics and professional responsibility has been included among the learning outcomes required of engineering education programmes in many counties. So, how should engineering ethics be taught? There is evidence - both within engineering education and more widely - that discussing dilemmas in formal education does lead to increases in measured moral reasoning ability. It has also been argued that ethical issues should not be taught as if they are only the individual responsibility of a particular engineer, but should rather be understood as embedded in a broader social and political context within which engineering decisions are taken. This may require more than the introduction of ethics courses; instead, it may require rethinking engineering education. The ‘hidden curriculum’ concept may be useful in this context. It suggests that, alongside the ‘formal curriculum’, students also learn some things implicitly through the social and organizational nature of their studies. Hence, discussion of dilemmas that do not have a single clear resolution can seem to students to be out of synch with the culture of engineering education which is often focused on narrowly technical solutions. Similarly, if assessment is highly competitive and individualistic, students may, implicitly, become more self-serving in their decision making. In such contexts, courses addressing ethical issues may be swimming against the cultural tide of the programme as a whole. This paper explores the role of the hidden curriculum in engineering education, drawing on quantitative data from a very large study of moral reasoning among engineering students (almost 1,000 participants with longitudinal test data at two time periods). The study also uses an innovative measure of moral reasoning (the Engineering and Science Issues Test), which was translated and used in a French language context for the first time.