The hidden curriculum within medical education has been a topic of recent debate. Consensus opinion regarding the continued relevance of this term, what constitutes the hidden curriculum, and the nature of its impact do not exist. Further research is required to contribute to this debate. This work sets out to investigate which factors beyond taught cognitive knowledge influence medical students in clinical and educational environments and examine how this occurs. Semi-structured focus group interviews were conducted with 39 students from one UK medical school. Fourteen faculty were interviewed individually to triangulate data. Data were analysed using constructivist thematic analysis, informed by grounded theory convention. The presence of the hidden curriculum was clearly demonstrated, acting through role modelling, organizational culture, stereotyping and professional dress. Mentioned frequently were the influences of the hidden curriculum on student professionalism and identity development. Professionalism was perceived as being negatively impacted by the hidden curriculum and seen as an imposition from senior faculty to control students. Students believe medical identity formation begins prior to medical school, in a process known as "anticipatory socialization", a previously unstudied identity transition. Students felt covert institutional agendas negatively impacted their identity, pushing them further from the identity their institution was encouraging them to acquire. Key messages for educators include the need to explore the hidden curriculum through discussion with students. Improving transparency of organizational culture may allow students to interpret institutional agendas in the way institutions formally intend, reducing orthogonal interpretations of organizational culture and subsequent impact upon identity formation.