SPINK5 (serine protease inhibitor Kazal-type 5), encoding the protease inhibitor LEKTI (lympho-epithelial Kazal-type related inhibitor), is the defective gene in Netherton syndrome (NS), a severe inherited keratinizing disorder. We have recently demonstrated epidermal protease hyperactivity in Spink5^−/− mice resulting in desmosomal protein degradation. Herein, we investigated the molecular mechanism underlying the epidermal defect in 15 patients with NS. We demonstrated that, in a majority of patients, desmoglein 1 (Dsg1) and desmocollin 1 (Dsc1) were dramatically reduced in the upper most living layers of the epidermis. These defects were associated with premature degradation of corneodesmosomes. Stratum corneum tryptic enzyme (SCTE)-like and stratum corneum chymotryptic enzyme (SCCE)-like activities were increased, suggesting that these proteases participate in the premature degradation of corneodesmosomal cadherins. SCTE and SCCE expression was extended to the cell layers where Dsg1 and Dsc1 immunostaining was reduced. In contrast, a subset of six patients with normal epidermal protease activity or residual LEKTI expression displayed apparently normal cadherin expression and less severe disease manifestations. This suggests a degree of correlation between cadherin degradation and clinical severity. This work further supports the implication of premature corneodesmosomal cadherin degradation in the pathogenesis of NS and provides evidence for additional factors playing a role in disease expression.