Introduction: Medical students moving abroad after qualification may contribute to domestic healthcare workforce shortages. Greater insights into how medical students make decisions about moving abroad may improve post-qualification retention. The aim was to develop a programme theory explaining medical students’ intentions to move abroad or not.

Methods: In Phase 1 the initial programme theory was generated from a literature review. In Phase 2, the theory was developed through 30 realist interviews with medical students from a medical school in the United Kingdom. In Phase 3 the final programme theory was used to produce recommendations for stakeholders.

Results: The findings highlight the complex decision-making that medical students undertake when deciding whether to move abroad. We identified five contexts and six mechanisms leading to two outcomes (intention to move abroad and no intention to move abroad).

Conclusions: This realist evaluation has demonstrated how contexts and mechanisms may interact to enable specific outcomes. These insights have allowed evidence-based recommendations to be made with a view to retaining graduates, including protected time within medical curricula to experience other healthcare systems, improved availability of domestic postgraduate posts providing domestic career certainty and stronger domestic-based social support networks for graduates.