Effective mentoring promotes the development and success of graduate students. Yet mentoring, like other relationships, can have negative elements. Little knowledge exists about the problematic mentoring that graduate students experience despite its potentially detrimental impacts. To begin to address this gap, we conducted an exploratory interview study to define and characterize negative mentoring experiences of 40 life science doctoral students. Students attributed their negative mentoring experiences to interacting factors at multiple levels--from interpersonal differences and poor relationship quality to issues at the research group, departmental, organizational, and discipline levels--all of which they perceived as harmful to their development. We found that doctoral students experienced forms of negative mentoring similar to those reported in workplace and undergraduate research settings, but they also experienced negative mentoring that was unique to academic research and their stage of development. Our results are useful to mentors for reflecting on ways their behaviors might be perceived, to mentees for avoiding situations that might be conducive to negative mentoring, and to programs and institutions for improving structures and processes to prevent negative mentoring. Our findings also serve as a foundation for future research on the prevalence and impacts of negative mentoring experiences in graduate education.