BACKGROUND: The process of Legitimate Peripheral Participation (LPP) within a community of practice framework (CoP) was used to explore graduate entry medical students' professional identity formation (PIF) during their first year of study. A conceptual model has been developed that can be used by medical educators to better understand PIF and to aid the explicit incorporation of PIF activity within the undergraduate curriculum. METHODS: Ten students from one UK medical school participated in the longitudinal study and were interviewed at three points during the first year. Semi-structured group interviews were used to explore students' experience of the clinical environment and the nature of their interactions with both clinicians and patients in a community-based medicine practice. The interviews were audio recorded and transcribed. Thematic analysis was used to identify overarching themes which are represented as facets in the model of PIF. RESULTS: Results demonstrate that students are legitimately peripherally participating within both medical student CoPs and wider medical CoPs. Themes identified within the narratives have allowed the development of a new model to understand PIF within the context of LPP in a CoP. This has five facets: Awareness, Collaboration, Negotiation, Evaluation and Realisation. Sophisticated reflection-in-action is shown to be an important aspect of PIF and enables a more conscious understanding of the change that is occurring in our students. CONCLUSION: PIF is a complex, non-linear process that is supported by reflection-in-action and early student introduction to clinical practice. It can be recognised in students' narratives in their changing use of language, their understanding of the medical COP, and their evolving relational participation with those around them. This study adds to those that have previously explored PIF. The model of PIF developed in this study illustrates how experiences in the clinical environment support PIF. Medical educators may find this model helpful when considering how PIF can be explicitly encouraged in the medical curriculum and how reflection may be used for the purpose of identity change.