To assess the prevalence of asthma, chronic bronchitis and respiratory symptoms, and to calculate risk factors for them, we performed a postal survey in Helsinki, the capital of Finland. During the spring of 1996, questionnaires were mailed to a random sample of 8000 individuals aged 20-69. The total response rate was 76%, with 6062 complete answers. The prevalence of having ever had asthma was 7.2%, physician-diagnosed asthma was 6.6% and physician-diagnosed chronic bronchitis was 3.7%. Asthma was significantly more common among women than men, but no gender differences existed in prevalence of chronic bronchitis. The most common respiratory symptom was sputum production when coughing, reported by 27%. During the previous 12 months, wheezing had occurred in 20% and attacks of shortness of breath in 13% of subjects. Generally, the prevalence of different respiratory symptoms were significantly higher among smokers. The most important risk factor for asthma was a family history of asthma (Odds ratio:OR 3.3). Multivariate analysis revealed that being a member of the socioeconomic group, manual workers, was associated with a significantly increased risk for chronic productive cough (OR 1.7), and for wheezing during the previous 12 months (OR 1.7). Manual workers of both genders had the highest prevalence of asthma, chronic productive cough and wheezing during the previous 12 months. The prevalence of asthma in Helsinki was higher than previously found in Finland, and was at a similar level to that of other Nordic countries. In contrast, prevalence of chronic bronchitis was lower than previously shown in Finland.