Background. The seasonality of asthma morbidity is well recognized. A peak in asthma exacerbations in September has been noted for years at our center. Objective. To examine the hypothesis that the increment in asthma exacerbations in September is influenced by the beginning of the kindergarten and school year. Methods. The monthly admission rate for asthma in patients of different ages was retrospectively evaluated in seven hospitals from various areas in Israel from January 2003 to December 2005. Results. Of the 408,242 hospital admissions during the study period, 8,011 were for asthma exacerbations: 4,091 in adults (1.3% of adult admissions) and 3,920 in children (3.8% of pediatric admissions). The asthma admission rates varied considerably throughout the year, with a peak of 4% of total admissions in the winter months and a nadir of 2% in the summer months. September was unique for its particularly high rate of admissions for asthma attacks in children (6% of total admissions), especially toddlers and the school-age group. In adults there was a progressive increase in asthma admissions from September through December without a unique peak in September. Conclusions. There is a characteristic increase in asthma exacerbations and admissions in September in the pediatric age group. This phenomenon might be explained by the increased exposure to respiratory viruses, to new allergen exposure in school or kindergarten, increased emotional stress due to start of the new school year, or poor compliance and withdrawal of treatment during the summer. Clinicians should consider administering prophylactic treatment for asthma in children before onset of the school year.