INTRODUCTION This paper argues that particular experiences in the workplace are more important than others and can lead to transformational learning. This may enable practitioners to cross 'vocational thresholds' to new ways of being. AIM A notion of 'vocational thresholds' is developed, aiming to help build an understanding of the most powerful learning experiences of general practitioners (GPs). Vocational thresholds takes its cue from the idea of 'threshold concepts' - concepts that transform perspectives and integrate previously disconnected or hidden knowledge, sometimes in ways that are 'troublesome' to previously held beliefs. METHODS The paper is based on a thematic analysis of 57 GPs' brief written accounts of a particularly powerful learning experience during their development. Accounts were provided in a conference session about an ongoing study of workplace-based structured learning arrangements in the fields of general practice medicine, engineering, and building. FINDINGS Most GPs' accounts focused on development of dispositional attributes that moved them to a new understanding of themselves in relation to their work and patients. Just under two-thirds picked out informal and formal collegial relationships within purposeful learning arrangements as pivotal. A third picked out direct experiences with patients as shifting their perspective. CONCLUSION The emergent idea of vocational thresholds is offered as a way to frame the most important learning experiences identified by GPs. It supports a focus in early and ongoing development beyond accumulating clinical expertise and skills (knowing and doing), to dispositional capability (being) - vital for practitioners negotiating inherent and daily uncertainty. KEYWORDS General practitioners; Medical education; Vocational education; Identity; Learning experiences; Threshold concepts.