The chances of serious intracranial and intra orbital is certainly more in revision surgery than in a primary case for endoscopic sinus surgery. This chapter emphasises the role of revision surgery in FESS. A detailed account is illustrated with profuse photographs of the intra operative, post operative and CT scan findings to show the problem areas in original surgery which unfortunately leads to revision surgery, when the patient is symptomatic in spite of intensive medical line of treatment. The importance of very thorough history from the patient to make sure that the symptoms are only sinus origin and not related to any other systemic problems. A detailed examination is mandatory to exclude any other pathology by means of specific investigations prior to any planning of revision surgery. A diligent nasal endoscopic examination along with high resolutions CT imaging and its interpretation is most important before deciding about revision surgery. Post operative follow up is also extremely important especially revision surgery is performed for adhesions obstructing natural ostia of the sinuses. The role of instruments such as thru’ cut forceps, microdebriders and laser have been discussed to minimise operative trauma and subsequent adhesions in the post operative period.