ImportanceThere is some data to suggest that racial and ethnic minority infants with congenital diaphragmatic hernia (CDH) have poorer clinical outcomes.ObjectiveTo determine what patient- and institutional-level factors are associated with racial and ethnic differences in CDH mortality.Design, Setting, and ParticipantsMulticenter cohort study of 49 US children’s hospitals using the Pediatric Health Information System database from January 1, 2015, to December 31, 2020. Participants were patients with CDH admitted on day of life 0 who underwent surgical repair. Patient race and ethnicity were guardian-reported vs hospital assigned as Black, Hispanic (White or Black), or White. Data were analyzed from August 2021 to March 2022.ExposuresPatient race and ethnicity: (1) White vs Black and (2) White vs Hispanic; and institutional-level diversity (as defined by the percentage of Black and Hispanic patients with CDH at each hospital): (1) 30% or less, (2) 31% to 40%, and (3) more than 40%.Main Outcomes and MeasuresThe primary outcomes were in-hospital and 60-day mortality. The study hypothesized that hospitals managing a more racially and ethnically diverse population of patients with CDH would be associated with lower mortality among Black and Hispanic infants.ResultsAmong 1565 infants, 188 (12%), 306 (20%), and 1071 (68%) were Black, Hispanic, and White, respectively. Compared with White infants, Black infants had significantly lower gestational ages (mean [SD], White: 37.6 [2] weeks vs Black: 36.6 [3] weeks; difference, 1 week; 95% CI for difference, 0.6-1.4; P < .001), lower birthweights (White: 3.0 [1.0] kg vs Black: 2.7 [1.0] kg; difference, 0.3 kg; 95% CI for difference, 0.2-0.4; P < .001), and higher extracorporeal life support use (White: 316 patients [30%] vs Black: 69 patients [37%]; χ21 = 3.9; P = .05). Black infants had higher 60-day (White: 99 patients [9%] vs Black: 29 patients [15%]; χ21 = 6.7; P = .01) and in-hospital (White: 133 patients [12%] vs Black: 40 patients [21%]; χ21 = 10.6; P = .001) mortality . There were no mortality differences in Hispanic patients compared with White patients. On regression analyses, institutional diversity of 31% to 40% in Black patients (hazard ratio [HR], 0.17; 95% CI, 0.04-0.78; P = .02) and diversity greater than 40% in Hispanic patients (HR, 0.37; 95% CI, 0.15-0.89; P = .03) were associated with lower mortality without altering outcomes in White patients.Conclusions and RelevanceIn this cohort study of 1565 who underwent surgical repair patients with CDH, Black infants had higher 60-day and in-hospital mortality after adjusting for disease severity. Hospitals treating a more racially and ethnically diverse patient population were associated with lower mortality in Black and Hispanic patients.