Tracheobronchial structural lesions present a considerable diagnostic challenge and workload to tertiary paediatrics. Bronchoscopy is the definitive way of confirming these diagnoses. Quantification of the size of lesions is important to the decision-making processes for management, yet this aspect of assessment has been left to subjective visual estimates of the size as there has not been a method developed that enabled quantitative measurement. The clinical profiles of children with these disorders have long been suspected to be worse than respiratory illnesses in normal children however this aspect has never been studied using objective criteria. The major hypothesis of this thesis is that structural lesions such as malacia disorders of the tracheobronchial tree result in significant respiratory morbidity that is a result of dose dependent crossectional area losses in lesions which improve with increasing age and management strategies. The aims of this thesis were i. to develop a methodology for objectively quantifing airway lesions using a paediatric bronchoscope ii. establish a cohort of children with airway lesions and quantitatively define the airway lesions and then longitudinally study these lesions and the respiratory illness profiles using validated scales of illness over a 2 year period.