Bronchoscopy is the gold standard for evaluating tracheomalacia; however, reliance on an invasive procedure limits understanding of normal airway dynamics. Self-gated ultrashort echo-time MRI (UTE MRI) can assess tracheal dynamics but has not been rigorously evaluated.This study was a validation of UTE MRI diagnosis of tracheomalacia in neonates using bronchoscopy as the gold standard. Bronchoscopies were reviewed for the severity and location of tracheomalacia based on standardized criteria. The percent change in cross-sectional area (CSA) of the trachea between end-inspiration and end-expiration was determined by UTE MRI, and receiver-operating curves were used to determine the optimal cutoff values to predict tracheomalacia and determine positive and negative predictive values.Airway segments with tracheomalacia based on bronchoscopy had a more than threefold change in CSA measured from UTE MRI (54.4 ± 56.1% vs 14.8 ± 19.5%; P  20% change in CSA) of tracheomalacia had good sensitivity (80%) but low specificity (64%) for identifying tracheomalacia based on UTE MRI, whereas a "strict" definition (> 40% change in CSA) was poorly sensitive (48%) but highly specific (93%).Self-gated UTE MRI can noninvasively assess tracheomalacia in neonates without sedation, ionizing radiation, or increased risk. This technique overcomes major limitations of other diagnostic modalities and may be suitable for longitudinal population studies of tracheal dynamics.