A 47-year-old woman presented to our hospital with a fever. Chest computed tomography (CT) showed infiltrative shadows, central bronchiectasis, and a mucus plug in the lingula and lower lobes of the left lung, suggesting allergic bronchopulmonary mycosis (ABPM). However, lung cancer first had to be ruled out based on the following findings: enlarged hilar and mediastinal lymph nodes; an elevated serum carcinoembryonic antigen (CEA) level, and high ¹⁸F-fluorodeoxyglucose (FDG) uptake in the hilar and mediastinal lymph nodes in positron emission tomography (PET)/CT. Bronchoscopy showed no malignant findings, and a final diagnosis of ABPM was made. After corticosteroid treatment, the hilar and mediastinal lymph nodes shrank, and the serum CEA level decreased. We present a case of ABPM with hilar and mediastinal lymphadenopathy, false-positive accumulation in FDG-PET/CT, and elevated serum CEA, which made it necessary to differentiate it from lung cancer.