The prevalence of asthma is increasing in Taiwan but data remain limited. The aim of this study was to determine the prevalence, severity, demographic and seasonal variations of asthma, rhinitis, and eczema in Taiwan. Using a one-stage stratified cluster random sampling, first grade (aged 6-8) and eighth grade (aged 13-15) students from Taoyuan, northern Taiwan, were invited to participate in this survey. The results showed a total of 6190 students, 3079 aged 6-8 and 3111 aged 13-15, completed this survey. In general, children aged 6-8 had significantly higher prevalence rates of diagnosed asthma, rhinitis, and eczema than children aged 13-15 (12.2%, 29.8%, and 10.2% vs. 9.6%, 18.3%, and 4.7%, respectively). Similarly, children aged 6-8 had significantly higher proportions of allergic symptoms, except for exercise-induced wheezing (5.8% vs. 17.8%, p < 0.0001). Among those with allergic disorders, children aged 6-8 presented a greater severity of wheezing attacks in the last 12 months. As regards gender, boys aged 6-8 had a significantly higher proportion of asthma or rhinitis symptoms than girls aged 6-8 but not in children aged 13-15. In children aged 6-8, asthma and rhinitis peaked in winter, especially in December. However, children aged 13-15 had two peaks (winter and summer) for asthma or rhinitis.