This guidance for the management of patients with rhinosinusitis and nasal polyposis has been prepared by the Standards of Care Committee (SOCC) of the British Society for Allergy and Clinical Immunology (BSACI). The recommendations are based on evidence and expert opinion and are evidence graded. These guidelines are for the benefit of both adult physicians and paediatricians treating allergic conditions. Rhinosinusitis implies inflammation of the nose and sinuses which may or may not have an infective component and includes nasal polyposis. Acute rhinosinusitis lasts up to 12 weeks and resolves completely. Chronic rhinosinusitis persists over 12 weeks and may involve acute exacerbations. Rhinosinusitis is common, affecting around 15% of the population and causes significant reduction in quality of life. The diagnosis is based largely on symptoms with confirmation by nasendoscopy. Computerized tomography scans and magnetic resonance imaging are abnormal in approximately one third of the population so are not recommended for routine diagnosis but should be reserved for those with acute complications, diagnostic uncertainty or failed medical therapy. Underlying conditions such as immune deficiency, Wegener’s granulomatosis, Churg-Strauss syndrome, aspirin hypersensitivity and allergic fungal sinusitis may present as rhinosinusitis. There are few good quality trials in this area but the available evidence suggests that treatment is primarily medical, involving douching, corticosteroids, antibiotics, anti-leukotrienes, and anti-histamines. Endoscopic sinus surgery should be considered for complications, anatomical variations causing local obstruction, allergic fungal disease or patients who remain very symptomatic despite medical treatment. Further well conducted trials in clearly defined patient groups are needed to improve management.