In this theoretical paper, we apply a social exchange framework to understand mentors' negative experiences. We propose a typology of costs, categorized according to psychosocial and career mentoring functions. Our typology generates testable research propositions. Psychosocial costs of mentoring are burnout, anger, and grief or loss. Career costs of mentoring include diminished reputation, decrease in productivity, and risk of ethical transgressions. The typology focuses on faculty in higher education because of the prevalence and importance of mentoring in that work setting. However, the typology may be extended to career arenas such as law, medicine, and the military. The theory presents a framework for acknowledging negative experiences and the costs associated with mentorship.