OBJECTIVE To determine (1) the prevalence of mentoring relationships for U.S. medical school junior faculty; (2) the quality of these mentoring relationships; (3) any variation by gender or race; and (4) the relationship between mentoring and junior faculty members' perceptions of institutional professional support; research-, teaching-, and clinical-skills development; allocation of time to professional activities; and career satisfaction. METHODS In 1995 a 177-item survey was mailed to 3,013 full-time faculty at 24 randomly selected U.S. medical schools stratified on an area of medical specialization, graduation cohort, and gender. Mentoring was defined as "dynamic reciprocal relationship between an advanced career incumbent (the mentor) and a junior faculty member (the protégé) aimed at fostering the development of the junior person/protégé." Because mentoring is most crucial for junior faculty, the study focused on mentoring relationships within the previous three years ("recent mentoring") for faculty who were not full professors. Chisquare tests, analysis of variance, and principal-components analysis were used to analyze the data. RESULTS In all, 1,808 (60%) of the 3,013 faculty surveyed, of whom 72% were junior faculty, returned completed questionaires. Fifty-four percent of the junior faculty had had a recent mentoring relationship. There was no significant difference between the men and the women faculty or between majority and minority faculty in the prevalence and quality of the mentoring relationships. The faculty with mentors rated their research preparation and research skills higher than did the faculty without mentors. Most of the women faculty (80%) and the minority faculty (86%) who had had mentors reported that it was not important to have a mentor of the same gender or minority group. CONCLUSIONS Mentoring relationships are prevalent in academic medicine and should be promoted to support the career growth of junior faculty.