The aim of the current study was to review the aetiology of non-cystic fibrosis (CF) bronchiectasis from two tertiary paediatric respiratory units in order to determine how often making a specific aetiological diagnosis leads to a change in management, and to assess the contribution of computed tomography (CT) in determining the underlying diagnosis. The case records of all patients who were diagnosed as having bronchiectasis by CT, currently being seen at the Royal Brompton Hospital and Great Ormond Street Hospital for Children (London, UK), were reviewed. All patients had undergone extensive investigations, and the underlying aetiology and the area of pulmonary involvement (as seen on CT) were recorded. A total of 136 patients were identified; there were 65 young males and the group median (range) age was 12.1 yrs (3.1-18.1). Immunodeficiency, aspiration and primary ciliary dyskinesia accounted for 67% of the cases. In 77 (56%) children, the identification of a cause led to a specific change in management. There was no association between aetiology and the distribution of CT abnormalities. In conclusion, immunodeficiency and other intrinsic abnormalities account for the majority of cases of non-cystic fibrosis bronchiectasis seen in the current authors' units. Computed tomography scans do not contribute towards identifying the aetiology and, most importantly, a specific aetiological diagnosis frequently leads to a change in management.