Background: The initiating mediators of T-helper 2 inflammation, often seen in eosinophillic chronic rhinosinusitis (CRS), remains poorly understood. Interleukin (IL) 25, IL-33, and thymic stromal lymphopoietin (TSLP) are epithelial-derived cytokines implicated in the initiation of T-helper 2 inflammation and eosinophilia in other diseases. The expression of these cytokines was compared with phenotypic and histopathologic markers to investigate the factors that may drive eosinophilic inflammation in CRS. Method: Sinus mucosal samples from patients with CRS who were undergoing sinus surgery as part of their management were analyzed for IL-25, IL-33, and TSLP messenger RNA (mRNA) expression by quantitative polymerase chain reaction. Patients with tumor and who were undergoing surgery via an endonasal approach with normal sinus mucosa were controls. The mRNA expression was compared with CRS phenotype and histopathologic measures of eosinophilic inflammation. Immunohistochemical staining was used to confirm mRNA expression. Results: Thirty-nine patients (mean ± standard deviation age; 48.2 ± 15.0 years, 38% women), 12 patients with CRS with nasal polyps, 20 patients with CRS without nasal polyps, and 7 controls were recruited. Higher IL-25 (p = 0.005) and IL-33 (p = 0.003) mRNA and protein expression was observed in patients with >10 eosinophil/hpf. TSLP showed no significant associations (p = 0.39). Similar overexpression was seen in eosinophilic dominated inflammation (IL-25, p = 0.01; IL-33, p = 0.02) and patients with greater inflammatory severity. Conclusion: IL-25 and IL-33 overexpression was observed in eosinophilic CRS, The release of these cytokines by dysfunctional endothelium may perpetuate the eosinophillic inflammation in CRS.