The Full Form of FESS is Functional endoscopic sinus surgery.

Functional endoscopic sinus surgery is a minimally invasive technique used to restore sinus ventilation and normal function. The most suitable candidates for this procedure have recurrent acute or chronic infective sinusitis, and an improvement in symptoms of up to 90 percent may be expected following the procedure. Fiberoptic telescopes are used for diagnosis and during the procedure, and computed tomography is used to assess the anatomy and identify diseased areas. Functional endoscopic sinus surgery should be reserved for use in patients in whom medical treatment has failed. The procedure can be performed under general or local anesthesia on an outpatient basis, and patients usually experience minimal discomfort. The complication rate for this procedure is lower than that for conventional sinus surgery.