Objectives: To determine changes in ethmoid, maxillary sinus and orbital volume following endoscopic sinus surgery. Methods: 45 patients were subjected to endoscopic sinus surgery for chronic sinusitis with or without nasal polypi. C.T scans done preoperative and 3 months postoperative, five ethmoidal measures (3 axial, 2 coronal) IOD 1-5, two maxillary measures (left and right), orbital measure (POE). Results: Postoperative CT scans demonstrate decrease in mean ethmoid cavity mainly at IOD 2 (mean decrease = -1.89). There is a decrease in maxillary measures (mean decrease = -1.89) and increase in POE by .37.