Engaging stakeholders during medical device design processes, especially during front-end design activities, is a critical consideration for successful product design, which includes the safety and effectiveness of devices. The use of prototypes with stakeholders is encouraged by proponents of human-centered design, but guidelines for front-end stakeholder engagement with detailed descriptions of prototyping practices are lacking. One important question design practitioners must ask for each stakeholder engagement is how many prototypes to use. This study investigated reasons design practitioners chose to use one or more prototypes to engage stakeholders during front-end design activities within their design projects. Participants described using multiple prototypes, for example, to allow stakeholders to compare across different design alternatives, and to convey to stakeholders that multiple alternatives are being explored. Participants described using a single prototype, for instance, to probe for deep responses about a narrow topic and to refine a single concept through feedback. These results have the potential to inform design decisions and pedagogical approaches to prototyping use.