ImportancePrevious studies have demonstrated sex-specific disparities in performance assessments among emergency medicine (EM) residents. However, less work has focused on intersectional disparities by ethnoracial identity and sex in resident performance assessments.ObjectiveTo estimate intersectional sex-specific ethnoracial disparities in standardized EM resident assessments.Design, Setting, and ParticipantsThis retrospective cohort study used data from the Association of American Medical Colleges and the Accreditation Council for Graduate Medical Education Milestones (Milestones) assessments to evaluate ratings for EM residents at 128 EM training programs in the US. Statistical analyses were conducted in June 2020 to January 2023.ExposureTraining and assessment environments in EM residency programs across comparison groups defined by ethnoracial identity (Asian, White, or groups underrepresented in medicine [URM], ie, African American/Black, American Indian/Alaska Native, Hispanic/Latine, and Native Hawaiian/Other Pacific Islander) and sex (female/male).Main Outcomes and MeasuresMean Milestone scores (scale, 0-9) across 6 core competency domains: interpersonal and communications skills, medical knowledge, patient care, practice-based learning and improvement, professionalism, and system-based practice. Overall assessment scores were calculated as the mean of the 6 competency scores.ResultsThe study sample comprised 128 ACGME-accredited programs and 16 634 assessments for 2708 EM residents of which 1913 (70.6%) were in 3-year and 795 (29.4%) in 4-year programs. Most of the residents were White (n = 2012; 74.3%), followed by Asian (n = 477; 17.6%), Hispanic or Latine (n = 213; 7.9%), African American or Black (n = 160; 5.9%), American Indian or Alaska Native (n = 24; 0.9%), and Native Hawaiian or Other Pacific Islander (n = 4; 0.1%). Approximately 14.3% (n = 386) and 34.6% (n = 936) were of URM groups and female, respectively. Compared with White male residents, URM female residents in 3-year programs were rated increasingly lower in the medical knowledge (URM female score, −0.47; 95% CI, −0.77 to −0.17), patient care (−0.18; 95% CI, −0.35 to −0.01), and practice-based learning and improvement (−0.37; 95% CI, −0.65 to −0.09) domains by postgraduate year 3 year-end assessment; URM female residents in 4-year programs were also rated lower in all 6 competencies over the assessment period.Conclusions and RelevanceThis retrospective cohort study found that URM female residents were consistently rated lower than White male residents on Milestone assessments, findings that may reflect intersectional discrimination in physician competency evaluation. Eliminating sex-specific ethnoracial disparities in resident assessments may contribute to equitable health care by removing barriers to retention and promotion of underrepresented and minoritized trainees and facilitating diversity and representation among the emergency physician workforce.