The symptoms of rhinosinusitis occur in a variety of sinonasal conditions, which may be broadly classified as allergic (seasonal, perennial or occupational rhinitis/rhinosinusitis) or non-allergic (caused by infection, or non-infectious, e.g. drug-induced or idiopathic). Correct diagnosis is important for optimal management. A thorough history should be taken, followed by general and endoscopic examinations and confirmatory investigations. Careful examination should reveal obvious alternative causes of symptoms, such as polyps or tumours. If allergy is suspected, this can be confirmed by further tests, particularly the skin-prick test or measurements of serum specific IgE. Imaging techniques, usually X-rays or CT scanning, are of use if a systemic condition or major sinonasal disorder needs to be excluded. Other useful diagnostic aids are measurements of nasal peak flow, rhinomanometry, acoustic rhinometry, olfactory threshold, and measures of mucociliary function (which may include biopsy for electron microscopy).