Allergic fungal rhinosinusitis is a subtype of chronic rhinosinusitis. It is characterized by an allergic reaction to non-invasive fungal infections causing severe inflammation and accumulation of thick mucin rich with eosinophils and fungi hyphae within the sinuses. This subset accounts for 8% of all chronic rhinosinusitis cases worldwide. The criteria for diagnosis include chronic rhinosinusitis, eosinophilic mucin on pathology, allergic reaction to fungi, lack of invasive fungal disease or immunodeficiency and characteristic hyperdense secretions seen on computed tomography. The mainstay therapy is endoscopic sinus surgery, which can be more challenging than that for chronic rhinosinusitis with higher rates of complications. Pre-operative systemic steroids and post-operative maintenance with saline irrigations and local nasal steroids are imperative for successful treatment.