Abstract Objective To measure and evaluate the effects of tracheal dimensions on survival and ventilation in a large series of infants with congenital diaphragmatic hernia (DCH) antenatally treated with fetal endulominal occlusion (FETO). Study design Tracheal dimensions on chest X-rays were measured by two blinded radiologists. Survival, day1 best oxygenation index (d1-BOI), duration of ventilation, CPAP and hospital stay were recorded. Survivors with minimum 12-month-follow-up were longitudinally compared for incidence of gastro-oesophageal reflux, chest infections, chest deformities and hernia recurrence. Results 70 infants with CDH (FETO, n=41) were treated between 2004 and 2010. Hernia repair was performed in 26 infants without FETO (patch repair=8) and 35 infants with FETO (patch repair=26; P=0.0015). Infants with FETO had wider trachea than those without FETO at T1 (P<0.0001) and between T1 and carina (P<0.0001). Tracheal diameter was similar in survivors and non-survivors within the FETO group. Tracheal size did not correlate with d1-BOI in infants with FETO (r2=0.17) and those without FETO (r2=0.07). There were no differences in days of mechanical ventilation (P=0.3), CPAP (P=0.2) and hospital stay (P=0.3). In the longitudinal study, tracheal widths were larger on last CXR than on preoperative ones in patients without FETO (T1, P=0.02; widest point, P=0.001; carina, P=0.0001), and for patients with FETO at widest point (P<0.0001) and at carina (P<0.0001), but not at T1 (P=0.12). The two groups showed no difference in the clinical variables. Conclusion FETO has a significant impact on tracheal size of infants with CDH. However, tracheal size does not impact survival or the requirement for early respiratory support.