CONTEXT: To earn society's trust, medical students must develop professional values and behaviours via a transformative process, from lay person to doctor. Yet students are expected to epitomise the values and behaviours of a doctor from the outset of medical school, leading them to feel 'judged all the time' (in terms of their professionalism). Our aim, therefore, is to extend knowledge exploring the expectations communicated to and perceived by medical students and to provide a conceptually framed understanding of students' associated emotional tensions. METHODS: We used a qualitative exploratory case study methodology within a constructivist paradigm to explore the messages communicated about professionalism and students' perceived expectations of professionalism in one medical school. Data were collected in the form of: (i) regulatory and medical school documents, and (ii) focus groups with 23 participants in their first 2 years at medical school. We used thematic analysis for data interpretation and two theoretical lenses, Amalberti et al.'s framework of system migration for health care and Sinclair's adaptation of Goffman's dramaturgical theory, to critically analyse the results. RESULTS: We found messages and perceived expectations of knowledge and competence, and the need to ensure trust. We also identified that the expectations of patients, doctors, society, family and friends are just as, if not more, influential than policy and regulatory expectations for early years' medical students. Moreover, we found tensions, with students feeling that the expectations of them from others were unrealistic for their level of training. With this came a sense of pressure to meet expectations that participants responded to by acting as if already competent. CONCLUSIONS: Our findings suggest that external forces (expectations) drive early years' students to act as if competent. Although this is part of student identity formation it could also have implications for patient safety and therefore necessitates recognition and support from educators.