It was previously believed that sinusitis lasting longer than 3 months might lead to irreversible disease. Experience with functional endoscopic sinus surgery indicates that this is rarely the case. Functional endoscopic sinus surgery describes an approach whereby target areas of obstruction are cleared of disease, which allows for ventilation of secondarily involved sinuses and return of mucociliary function. Although endoscopic sinus surgery is one of the techniques most frequently used to manage chronic sinus disease, it is not a suitable surgical approach for every otolaryngologist or all patient settings. Success with this endoscopic approach for chronic sinus disease is based primarily on rigorous perioperative medical care and postoperative surgical debridement. The greatest advancement that the nasal endoscope has brought to patient care is the ability to diagnose disease and follow objectively the effects of different treatment modalities. This advantage is recognized by allergists and used at several centers.