Voluntary employee turnover is of strategic importance for knowledge- intensive firms. Most of those firms have established mentoring programs devoted to providing protégés with psychosocial and career development support. Hence, the quality of relationships with mentors has a crucial impact on protégés’ intentions to leave the organization. This paper develops a fresh theoretical perspective that explains how and why one vital aspect of mentoring—mentor- protégé disagreement on relationship quality—affects turnover intentions over time. Drawing on the conservation of resources and leader-member exchange theories, we argue that growth in mentor- protégé disagreement positively affects increases in protégés’ turnover intentions. Our analysis of longitudinal data from a four- wave survey in a professional service firm supports this dynamic hypothesis. We also find that surface-level dissimilarity (in gender, but not age) positively relates to initial mentor-protégé disagreement, whereas deep-level dissimilarity (in future focus, but not present focus) positively relates to growth in mentor-protégé disagreement. Our study contributes to the literature on employee turnover by building theory and testing the extent to which mentoring represents a force embedding employees in their organization.