Despite concerns about the prevalence and ramifications of medical student mistreatment, the boundaries of faculty-student relationships have not been studied systematically in medical training programs. This study aimed to identify behaviours that occur with some frequency and potentially raise issues related to boundaries in the supervisor-trainee relationship. An anonymous questionnaire was distributed to the mailboxes of 154 residents in the departments of psychiatry, internal medicine, and obstetrics and gynaecology at four hospitals affiliated with Brown University Medical School. Residents were asked to report whether they had encountered specific behaviours from supervisors during medical training, the frequency of these experiences, and the professional status of the supervisor involved in each episode. There was a significant reported incidence of behaviours related to academic/professional boundaries, personal boundaries, and dating boundaries. Some of these behaviours raise issues related to exploitation. The major sources of these reported boundary behaviours were hospital-based clinical faculty, university-based academic faculty, and senior house staff. The potentially adverse effects of boundary behaviours on the individual student, the teacher-student relationship, and the doctor-patient relationship are discussed. Future research is recommended to clarify the limits of appropriate behaviour between supervisors and trainees in the medical learning environment