Twenty five patients with a clinical and radiological diagnosis of cystic fibrosis underwent high resolution Computed Tomography (HRCT) with the aim to study pulmonary parenchymal localization of disease. Both patients with initial pulmonary alterations and patients in a more advanced phase of the disease were studied. HRCT proved an excellent method for detecting very early lesions such as bronchiolar ectasia and bronchiolar obstruction by mucous accumulation. Moreover, HRCT proved to be very useful in detecting centrolobular and panlobular parenchymal lesions, with diagnostic information on axial and peripheral interlobular connective tissue. HRCT provided a better spatial definition of bronchiectasia and subpleural air if compared to conventional radiology. It also allowed for correct diagnosis of pneumothorax and detection of pleural fibrosis as a result of iatrogenic complications.