The aim of the study was to correlate the high-resolution computed tomography (HRCT) finding of high-attenuation mucus (HAM) impaction, including mean CT density and immunologic parameters in patients with allergic bronchopulmonary aspergillosis (ABPA). The institutional review board approved the study, and informed written consent was obtained. A total of 100 consecutive patients diagnosed with ABPA between June 2012 and December 2013 undergoing HRCT were enrolled. HRCT scan of the chest was evaluated for central bronchiectasis, mucoid impaction, and number of involved bronchial segments. Findings of mucoid impaction in patients were classified as HAM and non-HAM. CT attenuation values and mean CT density were calculated. Serologic parameters were assessed for total immunoglobin E (IgE), specific IgE, and absolute eosinophil count. Patients with HAM impaction on HRCT were found to have significantly higher levels of total IgE (P < 0.001), specific IgE (P = 0.03), and number of bronchial segments affected (P < 0.001). We found a CT density value of 70 Hounsfield units (HU) as an adequate cutoff value for HAM impaction. CT density >100HU is correlated with significantly higher values of serologic parameters. The present study suggests a relation between absolute HU values of HAM impaction and absolute value of serologic parameters in ABPA. Copyright © 2015 Mosby, Inc. All rights reserved.