Abstract Bronchial asthma is very common in childhood but the occurrence of wheeze with viral infections makes asthma difficult to diagnose in the pre-school child. Longitudinal studies suggest that there is a loss of airway function associated with early childhood asthma. Extrapolating from adult disease and the few tissue-based studies of children, this would appear to be related to abnormal postnatal development or remodelling of the airway walls. This appears to be associated with persistent airway inflammation without clinical evidence of airways obstruction. Abnormally thickened airways may be the mechanism underlying both bronchial hyper-responsiveness and fixed loss of respiratory function. The challenges for the future are to identify those children among the pre-school wheezers who will become asthmatic and to construct trials of therapies that may potentially prevent the development of clinical asthma or ameliorate the associated loss of airway function.