Endoscopic sinus surgery has progressed from a limited surgical intervention for chronic sinus disease to a viable approach for diffuse sinonasal polyposis, benign tumors, skull base defects, and orbital lesions. Some aspects of endoscopic diagnosis and treatment, however, remain controversial and are poorly understood. Controversies in endoscopic sinus surgery are reviewed and the primary critical issues with regard to the more recently developed instrumentation and the newer extended approaches are presented.