Background: Previous studies on the relationship between birth weight and childhood asthma have shown controversial results some studies refer to high birth weight and some to low birth weight as a risk factor for asthma. This study aimed to evaluate the prevalence of abnormal birth weight among the asthmatic children.

Materials and Methods: In this cross-sectional study, 400 asthmatic patients (age range, 5-15 years) referred to Kashan asthma and allergy clinic during 2007-2008 were allocated in to four groups based on birth weight.

Results: Sixty-two percent of asthmatic children had an optimal birth weight, 32.5% high weight, 1% very low weight and 4% low weight. In gender-based study of these children, 0.4% of boys had very low weight, 2.3% low weight, 63.7% optimal weight and 33.6% high weight among girls 1.7% very low weight, 6.2% low weight, 61% optimal weight and 31.1% high weight.

Conclusion: According to the results of the study, high birth weight is associated with asthma and among the children with abnormal birth weight, high birth weight has greater prevalence with similar results for both genders.