Background: Immunoglobulin (Ig) A represents a first-line defence mechanism in the airways, but little is known regarding its implication in upper airway disorders. This study aimed to address the hypothesis that polymeric Ig receptor (pIgR)-mediated secretory IgA immunity could be impaired in chronic upper airway diseases. Methods: Nasal and ethmoidal biopsies, as well as nasal secretions, were collected from patients with chronic rhinosinusitis (CRS) with (CRSwNP) or without nasal polyps (CRSsNP), allergic rhinitis (AR) and controls, and assayed for IgA1/IgA2 synthesis, pIgR expression, production of secretory component (SC), IgA and relevant IgA antibodies, and correlated to local eosinophils and inflammatory features (IL12, IL-13 and ECP). Results: pIgR expression was decreased in the ethmoidal mucosa in CRSwNP (p=0.003) and in AR (p=0.006). This pIgR defect was associated with reduced levels of SC (p=0.007) and IgA antibodies to Staphylococcus aureus enterotoxin B (SAEB) (p=0.003) in nasal secretions from CRSwNP patients, and with increased IgA deposition in subepithelial areas. pIgR downregulation was selectively observed in patients with tissue eosinophilia, whilst no clear relation to smoking history was observed. Conclusion: Epithelial pIgR expression is decreased in patients with CRSwNP and AR, and results in decreased SC and IgA antibodies to certain bacterial antigens (SAEB) in nasal secretions of CRSwNP patients in parallel to subepithelial accumulation of IgA. This defect in mucosal immunity is associated with eosinophilic, Th2-related inflammation.