Endoscopic sinus surgery has been reported to be successful, but lack of a standardized classification system hampers comparison of results between studies, and long-term results of surgery have not been reported in a series of consecutive patients. The results of our first 100 endoscopic sinus surgery procedures, reported previously after an average 9-month follow-up, were reviewed with the application of a new classification scheme and in light of a longer (4-year) follow-up. Surgery was successful in all patients whose sinus symptoms resulted from anatomical variations or suppurative infection, but failed in some patients with hyperplastic disease or polyps. In addition, the presence of reactive airway disease or the acetylsalicylic acid (ASA) triad was a bad prognostic sign. The overall success of the procedure in relieving sinus symptoms decreased from 98% at early follow-up to 91% at 4-year follow-up. Sixty-six percent were successful after one procedure and 25% required more than one procedure to achieve success. The decline in success since our first report in 1990 was mostly attributable to late failure in patients with recurrent symptomatic polyposis. Because symptoms may not recur in these patients for up to 3 years, long-term results of surgery for this disorder are necessary. Symptoms of recurrent polyposis can be controlled medically or by revision surgery.