BackgroundInformal peer learning is a particularly powerful form of learning for medical teachers, although it does not always occur automatically in the departments of medical schools. In this article, the authors explore the role of teacher communities in enhancing informal peer learning among undergraduate medical teachers. Teacher communities are groups of teachers who voluntarily gather on a regular basis to develop and share knowledge. Outside of medical education, these informal teacher communities have proved to be an effective means of enhancing peer learning of academic teachers. The processes underlying this outcome are, however, not known. This study therefore aims to explore the processes that make informal teacher communities effective in supporting peer learning of teachers.MethodsA qualitative study was performed at a Dutch medical school, where a student-centred undergraduate curriculum had recently been introduced. As part of this curriculum, tutors are segregated into separate specialty areas and thus have only limited opportunities for informal learning with other tutors. The authors followed two informal teacher communities aimed at supporting these tutors. They observed the interactions within the teacher communities and held semi-structured interviews with ten of the participants. The observation notes and interview data were analysed using thematic analysis.ResultsThe informal teacher communities allowed the tutors to engage in a dialogue with colleagues and share questions, solutions, and interpretations. The teacher communities also provided opportunities to explicate tacit expertise, which helped the tutors to develop an idea of their role and form a frame of reference for their own experiences. Furthermore, the communities enhanced the tutors’ sense of belonging. The tutors felt more secure in their role and they felt valued by the organisation due to the teacher communities.ConclusionsThis study shows that informal teacher communities not only support the professional development of tutors, but also validate and strengthen their identity as teachers. They seem to provide a dialogical space where informal intercollegiate learning is stimulated, stories are shared, tacit knowledge is made explicit, concerns are shared, and teacher identity is nurtured.Electronic supplementary materialThe online version of this article (doi:10.1186/s12909-016-0632-2) contains supplementary material, which is available to authorized users.