The new guidelines of the European Academy of Allergy and Clinical Immunology (EAACI) contained in the document European Position Paper on Rhinosinusitis and Nasal Polyps (EPOS) define chronic rhinosinusitis as the presence of two or more symptoms one of which is nasal obstruction/blockage/congestion or nasal secretion (frontal or postnatal), while other symptoms may include the presence of facial pain or pressure, or reduced or complete loss of the sense of smell provided that the symptoms last longer than twelve weeks. The diagnosis is based on a history of a supplemented clinical examination. Importantly, the clinical examination should include a rhinoscopy and endoscopy of the nose in order to assess the condition of mucosal secretions, the anatomical structure and the presence of polyps. Nasal swabs reveal causes and is followed by the administering of antibiotics in the exacerbation phase. If surgical treatment is indicated, a CT scan of the paranasal sinuses is to be conducted. CT scans reveal anatomical variations that are considered a predisposing factor along with allergies, immunodeficiency, microorganisms and a disorder in mucociliary transport. Surgical treatment is indicated if drug therapy is inadequate. Surgery can correct anatomical predisposing factors and expand the opening of the sinuses for their better ventilation and drainage. The first choice of surgical techniques is functional endoscopic surgery (FESS). The operation is usually focused on the ostiomeatal complex – an area of the meatus nasalis medius in which the front ethmoid, maxillary and frontal sinus are opened up. Ordinarily, a ethmoidectomy is carried out which involves removing the interetmoidal bone septa, also for better ventilation of the sinuses. If an endoscopy cannot remove the entire pathological problem, an open surgical approach is indicated for the paranasal sinuses.