Given the diversity of those affected by HIV, increasing diversity in the HIV biomedical research workforce is imperative. A growing body of empirical and experimental evidence supports the importance of strong mentorship in the development and success of trainees and early career investigators in academic research settings, especially for mentees of diversity. Often missing from this discussion is the need for robust mentoring training programs to ensure that mentors are trained in best practices on the tools and techniques of mentoring. Recent experimental evidence shows improvement in mentor and mentee perceptions of mentor competency after structured and formalized training on best practices in mentoring. We developed a 2-day "Mentoring the Mentors" workshop at UCSF to train mid-level and senior HIV researchers from around the country [recruited mainly from Centers for AIDS Research (CFARs)] on best practices, tools and techniques of effective mentoring. The workshop content was designed using principles of Social Cognitive Career Theory (SCCT) and included training specifically geared towards working with early career investigators from underrepresented groups, including sessions on unconscious bias, microaggressions, and diversity supplements. The workshop has been held three times (September 2012, October 2013 and May 2015) with plans for annual training. Mentoring competency was measured using a validated tool before and after each workshop. Mentoring competency skills in six domains of mentoring-specifically effective communication, aligning expectations, assessing understanding, fostering independence, addressing diversity and promoting development-all improved as assessed by a validated measurement tool for participants pre- and -post the "Mentoring the Mentors" training workshops. Qualitative assessments indicated a greater awareness of the micro-insults and unconscious bias experienced by mentees of diversity and a commitment to improve awareness and mitigate these effects via the mentor-mentee relationship. Our "Mentoring the Mentors" workshop for HIV researchers/mentors offers a formal and structured curriculum on best practices, tools and techniques of effective mentoring, and methods to mitigate unconscious bias in the mentoring relationship. We found quantitative and qualitative improvements in mentoring skills as assessed by self-report by participants after each workshop and plan additional programs with longitudinal longer-term assessments focused on objective mentee outcomes (grants, papers, academic retention). Mentoring training can improve mentoring skills and is likely to improve outcomes for optimally-mentored mentees.