INTRODUCTION: Like the fictional 'Accidental Tourist', an author who does not plan to write about travel, the accidental mentor is an experienced rural nurse who does not plan to be a mentor, and yet assumes that role with new or novice rural nurses as a result of them encountering a critical incident. Accidental mentoring is a short-term relationship that provides support for the new or novice nurse in managing the incident, while maintaining their level of confidence. This article describes the findings from a constructivist grounded theory study that examined Australian rural nurses' experiences of mentoring, including evidence for a new concept of mentoring - accidental mentoring. METHODS: Constructivist grounded theory is a research methodology that focuses on issues of importance for participants around an area of common interest - in this case Australian rural nurse mentoring. In this study, seven participants were interviewed, generating nine transcripts. These were analysed using a process of concurrent data generation and analysis. In addition, the literature regarding rural nurse workforce and mentoring was incorporated as a source of data, using collective frame analysis. RESULTS: Rural nurses live their work, which predisposes them to developing supportive relationships with new or novice rural nurses. Supportive relationships range from preceptoring, to accidental mentoring, mentoring and deep friendship, depending on the level of trust and engagement that is established between the partners and the amount of time they spend together. Accidental mentoring is a short-term relationship that is prompted by experienced rural nurses observing a new or novice rural nurse experiencing a critical incident. CONCLUSIONS: Findings are presented that illustrate a new concept of accidental mentoring not present in the current literature around nurse mentoring. A series of recommendations are included that suggest strategies for improved rural nurse retention as an outcome of recognising and developing such supportive relationships in the workplace. Strategies include: performance review and development processes that account for all forms of supportive relationships conducted in the workplace; recognising the importance of developing supportive relationships and allocating time for these; and continuing professional development designed to meet local needs for developing a culture of support in the workplace.