Chest computed tomography (CT) of a 76-year-old woman with bronchial asthma showed multiple lung nodules with high CT densities that were compatible with high-attenuation mucoid (HAM) impactions characteristic of allergic bronchopulmonary mycosis (ABPM). Follow-up chest CT revealed increased sizes of multiple lung nodules. However, a left upper lobe nodule showed lower CT density than the other HAM impactions. A transbronchial lung biopsy of that upper lobe nodule revealed lung adenocarcinoma. Measuring the CT density is important for the differential diagnosis of lung nodules when following ABPM patients. Our patient's increased serum carcinoembryonic antigen levels were associated with peripheral blood eosinophilia. Mucoid impaction in the lung was positively stained with carcinoembryonic antigen and showed the distribution of eosinophilic granules.