The patient was a 64-year-old female with a past medical history significant for pulmonary tuberculosis, and chronic hepatitis C. Thoracic radiation therapy (total dose of 60 Gy with parallel opposed-field irradiation) was performed for lung adenocarcinoma of the right middle lobe. Fever and a cough developed 6 months after the conclusion of radiotherapy and she was hospitalized in our department because of shadowing on chest computed tomography (CT). On admission, her vital signs were normal, and fine crackles were heard at the right lower lobe. Chest CT revealed consolidation outside the radiation field in the middle and lower lobes (Fig. 2A). Despite the administration of antimicrobial agents, her symptoms did not improve, and a bronchoscopy was performed. The findings from transbronchial lung biopsy were consistent with organizing pneumonia, although etiology was uncertain following blood testing, smear culture testing, and cytodiagnosis of the bronchoalveolar lavage fluid (BALF), we diagnosed her with organizing pneumonia induced by radiation therapy. She was not hypoxemic and, given her history of hepatitis C and tuberculosis, we opted to not use steroids in favor of observation only plus antitussive agents. The shadow continued to move, eventually crossing over to the other side, and completely disappeared in 5 months (Fig. 2B and C).