This paper is a report of a cross-sectional epidemiological study that formed part of multicenter European project; the aim was to estimate the prevalence of respiratory symptoms and signs related to asthma over a period of 12 months in the city of Seville. A sample of 4,000 persons of both sexes, aged between 20 and 44 years old, was surveyed first by mail questionnaire and later by telephone interview. We analyzed the response index obtained with the mail survey for the epidemiological study of asthma in the area and for the frequency of respiratory symptoms and their distribution by age and sex. The response index was 53.36% and was similar for men and for women. Forty-nine percent reported at least one respiratory symptom, with nocturnal coughing attacks (27.7%) and wheezing (22.2%) being the most frequent. The frequency of these symptoms was different by sex, however, with the former more often reported by women (p < 0.02) and the latter by men (p < 0.001). We found that 14.9% of the population had rhinitis and that women reported this symptom more often (p < 0.02). Symptoms related to asthma were nocturnal attacks of breathlessness, the use of asthma medication and an asthma attack diagnosed by a physician within the last 12 months. With these criteria the estimated prevalence of asthma was 11.72%, a proportion that held steady for all age groups except the middle-aged and for both sexes.(ABSTRACT TRUNCATED AT 250 WORDS)