Background: Inflammatory dysfunction is considered an important part of chronic rhinosinusitis (CRS). Corticosteroid therapy has been widely used in CRS. Effective topical delivery has been previously problematic. The post-endoscopic sinus surgery (ESS) corridor is essential for adequate topical drug access. Devices delivering large volume with positive pressure allow better distribution to sinus mucosa. The objective of this study is to evaluate the efficacy of postoperative topical sinonasal steroid irrigations for CRS. Methods: Patients with CRS undergoing ESS after failing previous medical therapy were recruited. Structured histopathology including markers of eosinophilia was performed. After surgery, patients received either budesonide 1 mg or betamethasone 1 mg delivered in a 240-mL squeeze bottle daily. Outcomes of the symptom score, Sino-Nasal Outcome Test 22 (SNOT-22) score, and endoscopy score were recorded. Results: A total of 111 patients (mean 50.1 ± 13.5 standard deviation [SD] years, 40.5% female) were included. Mean follow-up was 55.5 ± 33.9 weeks. Baseline and posttreatment symptom scores (2.6 ± 1.1 vs 1.2 ± 1.0), SNOT-22 scores (2.2 ± 1.1 vs 1.0 ± 0.8), and endoscopy scores (6.7 ± 3.0 vs 2.5 ± 2.0) revealed significant improvement (all, p < 0.001). Contrary to previous publications, patients with high tissue eosinophilia (>10/high power field [HPF]) had significantly more improvement on symptom score (1.9 ± 1.4 vs 1.1 ± 1.0, p = 0.04), SNOT-22 score (1.6 ± 1.3 vs 1.0 ± 0.8, p = 0.03), and endoscopy score (5.12 ± 3.4 vs 3.06 ± 3.0, p = 0.01) than those without. Conclusion: The philosophical approach to ESS in CRS is evolving. Topical therapies, when used appropriately, are highly effective for the most challenging eosinophilic patients. Although corticosteroid is a nonspecific therapy, it is effective when appropriately delivered.