Data in this chapter may be updated by a Medline search using the keywords: paediatric (pediatric) rhinosinusitis, sinusitis, complications, respiratory tract infections, immune deficiency, reflux, primary ciliary dyskinesia, cystic fibrosis, orbital cellulitis, endoscopic sinus surgery, adenoidectomy, and with particular reference to international consensus papers: the European Position Papers on Rhinosinusitis and Nasal Polyps (EPOS, 2007 and 2012). 1 , 2 The American Academy of Otolaryngology – Head and Neck Surgery (AAO-HNS) Consensus Statement on Pediatric Chronic Rhinosinusitis (2015) 3 and the International Consensus Statement on Allergy and Rhinology: Rhinosinusitis (ICAR:RS, 2016). 4 These documents have made use of multinational consensus expert opinion and consider the latest available evidence.