Patients with nasal polyps present repeatedly in otorhinolaryngology practices, but the prevalence of nasal polyps in the general population is not known. Our objective was to investigate the prevalence of nasal polyps in an adult Swedish population in relation to age, gender, asthma, and aspirin intolerance. A random sample of 1,900 inhabitants over the age of 20 years, stratified for age and gender, was drawn from the municipal population register in Skövde, Sweden, in December 2000. The subjects were called to clinical visits that included questions about rhinitis, asthma, and aspirin intolerance and examination by nasal endoscopy. In total, 1,387 volunteers (73% of the sample) were investigated. The sample size was adequate, with a good fit to the whole population. The prevalence of nasal polyps was 2.7% (95% confidence interval, 1.9-3.5), and polyps were more frequent in men (2.2 to 1), the elderly (5% at > or = 60 years of age), and asthmatics. Subjective symptoms of aspirin intolerance were not found to correlate with polyps. Nasal polyps were more common in adults than was stated by the a priori estimate. The Skövde population-based study is considered representative for the Swedish population.