OBJECTIVE The purpose of this study was to estimate the risk of bakers to develop asthma. METHODS A retrospective cohort study was performed among persons trained as bakers in Swedish trade schools in 1959-1989 (N = 2923). One group of referents (I) comprised persons who followed another program in the trade schools (N = 1258), and another (II) was randomly selected from the population register (N = 1258). A questionnaire on physician-diagnosed asthma, year of onset of asthma, asthma-like symptoms, consumption of antiasthmatic drugs, change of work due to asthma, familial atopy, and work history was mailed to all the participants. The incidence rates for persons trained as bakers were estimated separately for time as a baker and time in other occupations. RESULTS The response rate was about 75% in all three groups. There were no differences in the prevalence of asthma, asthma-like symptoms, consumption of antiasthmatic drugs, or familial atopy between the groups. Of the bakers, 2.5% had changed work due to asthma, significantly more than the referents (1.1% of reference groups I and II had changed, P < 0.05). The incidence rate for asthma among the men not working as bakers was 0.9-1.9 cases per 1000 person-years; male bakers had an incidence rate of 3.0. The relative risk for male bakers compared with all the referents was 1.8 (95% confidence interval 1.3-2.6). Women had an incidence rate of 2.3-3.0 cases per 1000 person-years, and there was no increased relative risk during work as a baker. CONCLUSIONS Male Swedish bakers, mainly those working during the 1970s and 1980s, have an approximately doubled risk to develop asthma.