Introduction and Background: Bronchial thermoplasty can be considered in the treatment of severe uncontrolled asthma, reducing smooth muscle mass and thus reducing bronchoconstriction, leading to a reduction in symptoms and better asthma control. We hypothesized that quantitative computed tomography (QCT) may show changes in airway dimensions and lung parenchyma after thermoplasty. Methods: 26 CT scans from 13 asthma patients (mean age 55y, range 35-79y) before and after thermoplasty were assessed retrospectively. CT scans were analysed by a fully automatic in-house software (YACTA). Wall thickness (WT), total diameter (TD) and percent wall thickness (WT%) were calculated per airway generation (G1-G10), and volume, mean lung density (MLD), emphysema index (EI), and air-trapping indices (RVC856-950, A1) were calculated per lobe and whole-lung. Results: Averaged parameters for generations G2-G4 showed a slight decrease in WT of 0.033mm (p=0.331) and an increase in TD of 0.42mm (p=0.192) resulting in a significantly lower WT% (p=0.031) after treatment. Mean lung volume decreased by 94 ml, showing most changes in both upper lobes [58 ml right (p=0.984), 120 ml left (p=0.893]. Air-trapping showed a tendency to decrease [RVC856-950 -0.059 (p=0.508), A1=-2.509 (p=0.127)]. Conclusion: QCT was able to show changes induced by thermoplasty in patients with severe asthma. A significant reduction in WT% is probably related to a reduction of smooth muscle cells as well as neuronal changes. QCT parameters could also show reduced hyperinflation resulting in lower lung volume and reduced air-trapping. More research is necessary to show the significance in a larger cohort.