This qualitative study of 29 physician mentors reports their perspectives on mentoring medical students in a well-respected medical school's formal, assigned, longitudinal mentoring program that has a curricular component in the second year. Using a phenomenologic inductive approach, common themes identified centered on mentors' relationships with their students and the characteristics of the relationships. Most mentors said their relationships solidified in the second year, where curricular responsibilities included teaching and evaluation. Mentors saw their roles change, yet relationships continued to develop as mentees advanced through medical school. They were surprised when students sought contact, support, and advice in years three and four of their programs. Mentors worried whether they "did enough" for their students, yet described their experiences and relationships as rewarding. Mentors subsequently found satisfaction in the continuing relationship during the clinical training years. The researchers note the importance of the curricular component for providing a purpose and structure for relationship development and in facilitating relationship development in this assigned mentoring program. (Contains 4 tables and 1 figure.)