One hundred and fifty-three patients with chronic sinusitis underwent endoscopic endonasal sinus surgery. They were preoperatively evaluated on the basis of their complaints, the severity of nasal polyps, X-ray findings, and axial and/or coronal CT scans. Postoperative degree of improvement in their complaints and endoscopic findings in the nasal cavity and sinus cavities were assessed. Most patients, including those with severe maxillary sinusitis, had a good postoperative course. The percentage of improvement in their complaints was 99.3%. Even in the case of olfactory disturbance, which is the most difficult symptom to treat, the percentage of improvement was 81.0%. There were only 8 patients with complaints and pathological findings in their nose or sinuses after the operation, 4 with allergic rhinitis and/or asthma, 1 with severe inflammation of the olfactory cleft, 1 with thickening of the bone in the sinuses after a 25-year history of sinusitis without treatment, and 2 with narrowing of the antrostoma at the middle meatus after the operation.