We encountered a case of pulmonary eosinophilic granuloma complicated with pneumothorax. A 24-year-old man was admitted to our department because of respiratory difficulty. Chest radiography on admission showed a right pneumothorax. A thoracic catheter was therefore inserted, and the pneumothorax was improved. A chest radiograph obtained after treatment showed diffuse linear reticular shadows; and a chest CT scan showed starlike nodular lesions and multiple cysts in the lungs, and a large nodule in the left rib. Because an ulcer had been diagnosed in the oral cavity 1 year previously, a mandible biopsy was performed, and a granulomatous lesion consisting of eosinophils was recognized. Taken together with the pulmonary findings, an eosinophilic granuloma was diagnosed. The patient was instructed not to smoke and the clinical course was observed. The pulmonary, mandibular, and costal lesions improved.