There is now increasing evidence that maternal factors may play a role in the development of asthma and asthma-related syndromes in children. For years it has been known that younger mothers are more likely to have children who develop wheezing illnesses in early life. It has been suggested that the development of the lung may differ in children of younger mothers compared to that in children of older mothers, but the biology of this association is not well understood. Recent data suggest that there is a much stronger association of allergic conditions in early life with allergic disease in the mother than in the father. Maternal asthma is more strongly associated with childhood asthma than is paternal asthma. The influence of the pattern of immune responsiveness in the mother on the ontogeny of the immune system in children needs further exploration, and it may offer new clues as to the factors determining the development of asthma and allergy in children.