What we know: Airway inflammation and remodelling of the airway wall play an important role in the pathophysiology of asthma in adults. There is a paucity of information regarding the pathology of asthma in early childhood. Postmortem and biopsy studies of children with asthma have consistently shown an increase in the size of mucous glands, but an increase in smooth muscle is seen only in some cases. Biopsy studies indicate that the airways of children with asthma are inflamed, although the infiltrate may be more lymphocytic than eosinophilic in nature. As children's lungs grow rapidly in the first few years, the impact of structural changes in the airways may have a more profound physiological impact at this time than later in life. What we need to know: Is the pathology of asthma the same in children and adults? Is it the same in mild, moderate and severe asthma? Can bronchoscopy and airway biopsy provide us with information about the pathology of early childhood asthma? Can the more advanced imaging techniques available today, such as spiral computed tomography and the use of inhaled gases of various densities, assist in elucidating the pathology of early childhood asthma? Can non-invasive techniques, such as measurement of exhaled gases, provide us with accurate information about inflammation and the pathology of early childhood asthma? What are the real ethical and practical limitations to studying the pathology of early childhood asthma?