What is the significance of closure in mentoring relationships? This small-scale study explores mentors' reflections on coming to closure in preparing to end long-term mentoring relationships. It was conducted during the final term of mentoring on a three-year accredited national programme aimed at supporting the learning and development of early career teachers in Wales. A reflexive confessional methodology was used to collect qualitative data from thirty-seven mentors regarding their plans for closure and the rationales for their preparations within a high-stakes mentoring context. A conceptual framework for the study was based on an evolutionarily framework of mentoring. Priorities for action and underpinning principles to bring about effective closure with mentees are identified. Preparing for closure is a frequently under-estimated responsibility of mentoring. We conclude that closure is a mentoring practice characterised by distinct behaviours and actions. These are both formal and informal, some located within a final mentoring 'phase' that is time-limited, while others are transitional, spanning the end of the formal relationship and post-mentoring relations. We suggest the final mentoring phase should be reconceptualised to take account of actions that indicate an on-going investment in professional capital that exceeds the time frame of the mentoring relationship.