There are many reports that state that the distribution and pattern of bronchiectasis may be sufficiently characteristic for a specific cause to be suggested. The aim of this study was to determine whether experienced chest radiologists could confidently and accurately diagnose various aetiologies of bronchiectasis from the computed tomography (CT) pattern of disease alone. CT scans of 108 patients with bronchiectasis of various causes (67 with idiopathic bronchiectasis, 10 with allergic bronchopulmonary aspergillosis, 12 with syndromes of impaired mucociliary clearance, 12 with hypogammaglobulinaemia and seven with adult cystic fibrosis) were assessed by three chest radiologists without knowledge of clinical data. Each observer listed the three most likely diagnoses in order of probability. In addition, a level of confidence on a 3-point scale was assigned to the first choice diagnosis. A correct first-choice diagnosis was made in 45% of readings. A high confidence level was given in only 9% of the first choice readings. Of these, a correct diagnosis was reached in 35%. There was poor interobserver agreement (mean kappa = 0.20). In conclusion, we found that the causes of bronchiectasis cannot be reliably diagnosed on the basis of CT appearances alone.