We carried out a retrospective cohort study using a self-administered questionnaire to assess the risk of hairdressers to develop asthma and chronic bronchitis. A representative sample of 4433 female hairdressers and an equal number of shop personnel in employment in 1980 was drawn from the Longitudinal Census Data File of Statistics Finland. Physician-diagnosed asthma, chronic bronchitis, and other respiratory diseases in 1980 and 1995 were inquired about in the respiratory part of the questionnaire. The response rate to the questionnaire was 82% for the hairdressers (n = 3484) and 79% for the referents (n = 3357). The prevalence of asthma among the hairdressers was 5.6% in 1980 and 10.1% in 1995, and the prevalence of chronic bronchitis was 3.9% in 1980 and 5.6% in 1995. The relative risk for asthma (odds ratio [OR]: 1.7, 95% confidence interval [CI]: 1.3 to 2.3 in 1980; and OR: 1.7, 95% CI: 1.4 to 2.2 in 1995) and for chronic bronchitis (OR: 2.2, 95% CI: 1.5 to 3.2 in 1980; and OR: 1.9, 95% CI: 1.4 to 2.6 in 1995) among hairdressers was almost twice that in the reference group. The incidence rate of asthma in 1980 through 1995 was 2.2 and of chronic bronchitis was 1.1 cases per 1000 person-years among hairdressers, whereas the rate in the reference group was 1.3 asthma cases and 0.9 chronic bronchitis cases per 1000 person-years. The relative risk for developing asthma during the 15 years' observation time was 1.7 (95% CI: 1.1 to 2.5) and for chronic bronchitis was 1.2 (95% CI: 0.7 to 1.9) among hairdressers, compared with referents. Our results indicate that hairdressers are at higher risk for developing asthma.