Since its inception in 2016, the establishment of learning communities led by senior Society of Behavioral Medicine (SBM) members has been central to the SBM's Mid-Career Leadership Institute (Institute). At the beginning of an initial two-day intensive workshop, groups of approximately six fellows are placed together, and one or two senior SBM members are asked to lead group mentoring. Senior SBM members serve as mentors during quarterly calls that are conducted over the year in order for group members to develop and present an individual leadership project at the following annual meeting. Group mentoring relies on the social dynamic that emerges from the group's own social norms and roles; it is designed to advance the careers of group members. To our knowledge, this is the first commentary describing a program of formal group mentoring for mid-career leadership development in a professional association. Based on the authors' experience as mentors, thematic and descriptive analyses of the initial workshop evaluations, and contemporaneous notes, we discuss the structure, process, and project outcomes of the formal group mentoring in SBM's Institute. Early process evaluation of the Institute suggests that the Fellows benefitted from the group mentoring experience.