In 1987, we studied the prevalence of asthma and rhinoconjunctivitis in 1112 grade-eight students in the town of Umeå, northern Sweden. The present study is based on the same cohort, reinvestigated in 1991. We aimed to estimate the changes in the prevalence of asthma and rhinoconjunctivitis and to examine some presumed risk factors of asthma and rhinoconjunctivitis. A postal questionnaire on present asthma, rhinoconjunctivitis, symptoms from the upper and lower airways, and the need for medication was used. Questions about living conditions, smoking, and present education were also included. The questionnaire was answered by 89% (990) of the subjects. The prevalence of self-reported asthma was 10.8% (boys 7.9%, girls 13.7%). The incidence rate/year was 1.1%, the remission rate/year was 5.7%, and the relapse rate/year was 10%. The risk factors for developing asthma appeared to be atopy, having a family history of asthma or rhinoconjunctivitis, and smoking. The prevalence of self-reported rhinoconjunctivitis was 14.3% (boys 15.6%, girls 13.1%). The incidence rate/year was 1%, the remission rate/year was 22%, and the relapse rate/year was 11%. Stopping smoking and having no family history of rhinoconjunctivitis or asthma appeared to favor remission in rhinoconjunctivitis.