Obesity and asthma are public health priorities in developed countries. Genes which may contribute to the control of both conditions include those encoding for the β2-adrenergic receptor, tumour necrosis factor-α (TNF-α) and the insulin-like growth factor 1 (IGF-1). Prospective studies consistently supported a link between obesity and reported wheezing or asthma diagnosis in children. However, there are still no clear explanations for such a link. On one hand, overweight asthmatic children may perceive their asthma as worse. On the other hand, atopic sensitization and bronchial hyper-reactivity do not explain the observed associations. After puberty, the association between asthma and obesity tends to be stronger in girls than in boys. It is conceivable that severe obesity in adolescent females may aggravate asthma through mechanisms different from those linking prepubertal obesity to unremitting asthma in males. Future studies should therefore address multiple age- and gender-specific hypotheses about the mechanisms that link obesity to asthma throughout childhood.