Allergic bronchopulmonary aspergillosis (ABPA) is a destructive disease of the lung characteristically associated with central bronchiectasis. This study was designed to determine if high-resolution computerized tomography (CT) could be used to define bronchiectasis in patients with suspected disease. Sixteen patients with asthma were studied. All demonstrated immediate cutaneous reactivity to common aeroallergens including Aspergillus fumigatus. Eight patients had clinical and immunologic evidence of ABPA. Six to 12 high-resolution CT sections (1.5 mm) were obtained at 1- to 2-cm intervals from the aortic knob to the dome of the diaphragm. All radiographs were evaluated separately by two readers in a blinded fashion and graded as to the presence and type of bronchial dilatation and bronchial wall thickening. Bronchial dilatation was seen in 41% of lung lobes in the ABPA group compared to 15% in the non-ABPA asthmatic control group. Upper lobe involvement and bronchial wall thickening was common to both groups. The presence of bronchiectasis in the control group may indicate that asthma is a more destructive lung disease than is currently appreciated. High-resolution CT of the chest has been shown in previous studies to have a sensitivity and specificity approaching that of bronchography, and the current findings support its use in the detection of bronchiectasis in patients with asthma suspected of having ABPA.