The "bronchial remodeling" specific for the asthmatic disease consists in irreversible changes of the bronchial wall, including glandular and smooth muscle fibers hyperplasia and÷or hypertrophy, goblet cells hyperplasia, and thickening of basement membrane (BM). We aimed to analyze the BM thickness in asthma patients, in order to validate the relationship between its changes and the disease severity defined in agreement with the Global Initiative for Asthma (GINA) criteria. The study group has been formed of 38 patients with different degrees of severity of asthma established by spirometry using Forced Expiratory Volume in one second (FEV1), and two patients without asthma symptoms as controls. The specimens harvested by fibrobronchoscopy have been processed by paraffin embedding followed by Hematoxylin-Eosin (HE) and Periodic Acid-Schiff (PAS) staining. For each case, the BM measurement has been realized by a "point-by-point" method. Statistical analysis has been performed using SPSS 17 software, by applying non-parametric correlation tests. The quantitative assessment revealed a progressive increase in BM thickness during the course of the disease, from a mean value of 11.2 μm in stage 1 to that of 15.6 μm in stage 4. Even if this process has been noticed starting with the first stage of asthma, the differences in the BM size were statistically significant only for stages 1 and 3 (p=0.047), stages 1 and 4 (p=0.000), stages 2 and 3 (p=0.000), and stages 3 and 4 (p=0.000). Spearman's test has shown an opposite correlation between the BM thickness and asthma severity defined by FEV1 values (r=-0.86, p<<0.01, 95% CI). Our study demonstrates that the collagen deposition at the epithelium-connective interface is initiated in early stages of asthma and continues in a progressive modality, the BM thickening being correlated with the disease severity. Thus, we support the concept of biological consequences of BM thickening in asthma pathogenesis, a mechanism still incompletely deciphered.