Correctional healthcare providers limited cultural and clinical competence to care for transgender patients represents a barrier to care for incarcerated transgender individuals. The present study aimed to adapt, deliver, and evaluate a transgender cultural and clinical competence intervention for correctional healthcare providers. In the summer of 2016, a theoretically-informed, group-based intervention to improve transgender cultural and clinical competence was delivered to 34 correctional healthcare providers in New England. A confidential survey assessed providers cultural and clinical competence to care for transgender patients, self-efficacy to provide hormone therapy, subjective norms related to transgender care, and willingness to provide gender-affirming care to transgender patients before and after (immediately and 3-months) the intervention. Linear mixed effects regression models were fit to assess change in study outcomes over time. Qualitative exit interviews assessed feasibility and acceptability of the intervention. Providers willingness to provide gender-affirming care improved immediately post-intervention (β=0.38; SE=0.41, p<0.001) and from baseline to 3-months post-intervention (β=0.36; SE=0.09; p<0.001; omnibus test of fixed effects χ=23.21; p<0.001). On average, transgender cultural competence (χ=22.49; p<0.001), medical gender affirmation knowledge (χ=11.24; p=0.01), self-efficacy to initiate hormones for transgender women, and subjective norms related to transgender care (χ=14.69; p=0.001) all significantly increased over time. Providers found the intervention to be highly acceptable and recommended that the training be scaled-up to other correctional healthcare providers and expanded to custody staff. The intervention increased correctional healthcare providers cultural and clinical competence, self-efficacy, subjective norms, and willingness to provide gender-affirming care to transgender patients. Continued efforts should be made to train correctional healthcare providers in culturally and clinically competent gender-affirming care in order to improve the health of incarcerated transgender people. Future efficacy testing of this intervention is warranted.