The seasonality of asthma exacerbations may reflect varying exposure to triggers. This study retrospectively analyzes the seasonality of asthma hospital admissions, at all ages, in a population-based study. Analysis of the seasonality of asthma admissions and correlation with temperature was carried out in the setting of a regional hospital covering all acute asthma admissions in an island population. Admissions were divided into pediatric (1994-8) and adult (1989-8) cases. Both pediatric (0-14 years; n = 2916) and adult (15-59 years; n = 1269) admissions showed a peak in January and a trough in August. The seasonality in pediatric admissions was far more pronounced than in adults. Both cohorts exhibited a second, smaller peak in spring. In school-aged children, the end of school in June was associated with a sharp (91%) drop in admissions, and restarting school in October was associated with an even sharper rise (165%). A negative correlation was found between admissions and mean monthly ambient temperatures, and this was most pronounced in the pediatric age groups. This marked seasonality may indicate that temperature is a proxy for the total time spent indoors. Both the start and end of school had a profound impact on pediatric admission rates. Prospective studies are necessary to establish the role of viral infections and the influence of indoor and outdoor aeroallergens on the seasonality of hospitalization rates for asthma in the local setting.