Context: The objective of this research was to explore medical students’ experience of challenges to their ethical knowledge and understanding in clinical practice, and to investigate their need and preference for support when faced with such challenges.Methods: We carried out a cross-sectional survey using web-based and paper questionnaires. Questions were designed using examples of ethical challenges identified in the previous literature. The study involved 3 UK university medical schools. All incorporate ethics teaching programmes in problem-based learning curricula. Participants were 732 (30% of total) senior undergraduate medical students learning within the clinical environment.Results: Students regularly experienced situations in clinical teaching settings that challenged their ethical values. Despite self-reports of good levels of confidence in their knowledge of ethical principles, medical students reported low levels of confidence in their ability to address these challenges, and perceived a need for additional support from clinical teachers.Conclusions: Complex and ethically challenging situations occur commonly in medical education. Many students feel that they do not currently access sufficient support from staff to address these. Clinical teachers were identified as the most relevant providers of guidance. The nature of medicine and its delivery makes it highly likely that medical students will come into contact with ethically challenging situations. Appropriate educational provision therefore requires medical educators to be equipped with the knowledge and the skills to engage with students’ ethical concerns.