Aim: To evaluate the criteria for diagnosing allergic fungal sinusitis and to maintain permanent drainage and ventilation, while preserving the integrity of mucosa. Methods: This is a prospective study of 251 patients with chronic rhinosinusitis with or without polyposis, of whom 199 were treated surgically. Mucus sample collection, nasal secretion culture, surgical specimen handling and histological evaluation of surgical specimens are described. The management included wide local endoscopic sinus debridement, adequate sinus aeration, post-operative use of steroids and antifungal therapy. Results: Fungal cultures of nasal secretions were positive in 201 (80.01 per cent) of 251 patients. Of the 199 surgical cases, fungal elements were found in 156 histological specimens (62.1 per cent). Allergic mucin was found in 182 patients (91.45 per cent). Nasal obstruction and proptosis were the commonest presentations. All pre-operative versus post-operative changes in AFS-associated complaints reached statistical significance of p < 0.001. The ethmoid sinus was commonly involved with adjacent lamina papyracea exhibiting demineralization in 26.6 per cent of cases. Intracranial extension was seen in 15 cases. Recurrence was noted in 11 cases. Conclusion: Comprehensive treatment with endoscopic sinus surgery, steroids and antifungal therapy is needed. AFS is readily recurrent. Long-term follow up is important.