Background: Primary health care (PHC), of which preventive medicine (PM) is a subspecialty, will have to cope with a deficiency of staff in the future, which makes the retention of graduates urgent. This study was conducted in Vietnam, where PM is an undergraduate degree in parallel to medical training. It aims to identify facilitating and hindering factors that impact recruitment and retention of PM graduates in the specialty. Methods: A cross-sectional study enrolled 167 graduates who qualified as PM doctors from a Vietnamese medical school, between 2012 and 2018. Data were collected via an online questionnaire that asked participants about their motivation and continuation in PM, the major life roles that they were playing, and their satisfaction with their job. Multiple regression analyses were used to identify which life roles and motivational factors were related to the decision to take a PM position and to stay in the specialty, as well as how these factors held for subgroups of graduates (men, women, graduates who studied PM as their first or second study choice). Results: Half of the PM graduates actually worked in PM, and only one fourth of them expressed the intention to stay in the field. Three years after qualification, many graduates had not yet decided whether to pursue a career in PM. Satisfaction with opportunities for continuous education was rated as highly motivating for graduates to choose and to stay in PM. Responsibility for taking care of parents motivated male graduates to choose PM, while good citizenship and serving the community was associated with the retention of graduates for whom PM was their first choice. Conclusions: The findings demonstrate the importance of social context and personal factors in developing primary care workforce policy. Providing opportunities for continued education and enhancing the attractiveness of PM as an appropriate specialty to doctors who are more attached to family and the community could be solutions to maintaining the workforce in PM. The implications could be useful for other less popular specialties that also struggle with recruiting and retaining staff.