In a retrospective study of 445 patients with nasal polyps, 95 (21 per cent) had asthma. Forty-two (44 per cent) of the patients with asthma had been skin tested and 27 (60 per cent) had positive reactions. Nasal polyps were twice as common in men as women, though a woman with nasal polyps was twice as likely to have asthma as a man. The average age of onset of polyps was 39 years and of asthma was 38 years. No significant difference was found in the age of onset of polyps or asthma in various groups of patients. Two per cent of all the patients in the series had nasal polyps, asthma and hypersensitivity to aspirin (the ASA triad). Ten per cent of those with polyps and asthma were hypersensitive to aspirin and thus had the full triad. Overall, 6 per cent of all the patients in the series were recorded as being allergic to aspirin. Asthma developed more commonly before polypectomy than after in the ratio of 2.5:1. Around 1 per cent of first polypectomies and 0.5 per cent of all polypectomies were followed by the development of asthma within a few months. The onset of asthma was found to occur most frequently just before or just after the first polypectomy. Those who developed asthma after polypectomy had significantly more polypectomies than both non-asthmatics and those whose asthma preceded their polyps. Though it is possible polypectomy may on rare occasions precipitate asthma, it is felt that it does not cause it.