To investigate if the lack of sex diversity in adult cardiothoracic anesthesiology fellowships is a result of few female applicants or low acceptance rate. Retrospective review of adult cardiothoracic anesthesiology applicants and fellows by sex and geographic regions across the United States. Accreditation Council for Graduate Medical Education's adult cardiothoracic anesthesiology fellowship programs across the United States. Applicants to adult cardiothoracic anesthesiology fellowship programs and fellows. No intervention. Numerical comparison of male and female applicants by percentage and acceptance rates into adult cardiothoracic anesthesiology fellowship programs in each geographic region. Women comprised between 27% and 35% of applicants from 2013 to 2018. Acceptance rates for men completing residency in the Midwest region ranged between 67% and 84%, and 67% and 87% for women from the Midwest (p = 0.1-0.9). Men from Northeast residencies had acceptance rate of 71% to 86% and women had rate of 69% to 83% (p = 0.2-0.8). Male and female residents from the Southeast had acceptance rates of 65% to 94% and 71% to 93%, respectively (p = 0.3-0.8). The male residents from the Southwest had acceptance rates of 73% to 85%, and female residents had rates between 44% and 100% (p = 0.02-0.8). The male residents from the West had rates of 59% to 88%, female residents had rates between 64% and 100% (p = 0.1-0.7). There is an absence of clear identification of the barriers preventing women from entering cardiac anesthesiology. The reasons leading to a male-dominated field of cardiac anesthesiologists stem from fewer female anesthesiology residents applying to cardiothoracic anesthesiology fellowships. No bias against acceptance of women into cardiothoracic anesthesiology fellowships was found. Copyright © 2021 Elsevier Inc. All rights reserved.