PURPOSE: To measure tracheal dimensions in children with congenital diaphragmatic hernia (CDH) who had undergone fetoscopic endoluminal tracheal occlusion (FETO) or were treated expectantly during gestation. MATERIALS AND METHODS: The study was approved by the local ethics committee. Computed tomography was performed in 23 patients (14 boys and nine girls) aged 1 month to 6.5 years, and the anteroposterior diameter, width, area, and perimeter of the trachea were determined. Seven of the 23 patients had undergone FETO and 16 had been treated expectantly. The relative difference of each parameter between the two most proximal concentric sections of the trachea, just below the larynx, and the two sections on which the trachea was the largest was compared between both groups (Mann-Whitney U test). Regression statistics were applied to maximum and mean tracheal areas as a function of age. Each trachea was divided into quartiles, and mean areas normalized to 3 years of age were analyzed for each quartile as a function of its relative position on the trachea (Student t test). RESULTS: Tracheal width, area, and perimeter were significantly different between both groups. A linear relationship was observed between the maximum and mean tracheal areas and age for both the FETO group (maximum tracheal area: R(2) = 0.83, P = .0045; mean tracheal area: R(2) = 0.92, P = .0005) and the non-FETO group (maximum tracheal area: R(2) = 0.66, P = .0001; mean trachea area: R(2) = 0.66, P = .0001). The maximum tracheal area in both groups tended to decrease toward the age of 5 years. Significantly different mean tracheal areas per tracheal quartile (P < .05) were found for all quartiles except for the proximal one-fourth. CONCLUSION: The relative difference between proximal and largest tracheal width, area, and perimeter was significantly larger in patients who underwent FETO than in those treated expectantly, demonstrating tracheal dilatation in the former. Measurements of tracheal dimensions at different levels indicate a maximum dilatation in the lower half of the trachea, which tends to level off toward the age of 5 years.