We attempted to determine the efficacy of endoscopic sinus surgery in adult patients with asthma and chronic rhinosinusitis or nasal polyposis. Fifty asthmatic patients from 17 to 74 years of age with a history of either chronic rhinosinusitis or nasal polyposis were examined. Sinonasal disease was confirmed endoscopically and with computerized tomography, and all had failed aggressive medical management of their sinonasal disease before undergoing endoscopic sinus surgery performed by the same surgeon in all cases. The following were compared for 12 months: preoperative and postoperative overall asthma control, peak flow measurements, asthma medication requirements, including the use of oral steroids, and hospitalizations for asthma. Twenty patients felt that their asthma control had improved postoperatively. Twenty per cent used less steroid inhaler, and 28% less bronchodilator inhaler. Of those 23 patients measuring peak flows, seven achieved higher levels and seven noted fewer dips and swings. Significant reductions in oral steroid requirements (p < 0.001) and hospitalization for asthma (p < 0.025) were also recorded postoperatively. Irrespective of whether the patient had chronic rhinosinusitis or nasal polyposis, both groups improved postoperatively. The commonest symptoms experienced by the group as whole and by the nasal polyposis patients were hyposmia and nasal obstruction. Postnasal discharge and headache were more important in the chronic rhinosinusitis group. Mean visual analog scores improved for all symptoms; in particular for nasal obstruction and sense of smell. Aggressive management of sinonasal pathology can improve asthma status. No major differences were recorded for outcomes when comparing patients with chronic rhinosinusitis or nasal polyposis; in particular there was no evidence for a worsening of asthma after nasal polypectomy.