Radiation therapy is used to treat many intrathoracic and chest wall malignancies. A variety of changes may occur after radiation therapy to the thorax. Radiation therapy produces dramatic effects in the lung. Pulmonary necrosis is an uncommon, severe, late complication of adjuvant postoperative radiation therapy. Bronchiolitis obliterans with organizing pneumonia is a distinct clinicopathologic entity characterized by patchy, migratory, peripheral air-space infiltrates. Radiation therapy can also cause spontaneous pneumothorax, mesothelioma, and lung cancer. In the mediastinum, radiation therapy may cause thymic cysts, calcified lymph nodes, and esophageal injuries. Cardiovascular complications of radiation therapy are often delayed and insidious. Premature coronary artery stenosis occurs after radiation therapy to the mediastinum. Radiation therapy may also give rise to calcifications of the ascending aorta, pericardial disease, valvular injuries, and conduction abnormalities. Women who undergo thoracic irradiation before the age of 30 years have a high risk of developing a second breast cancer. Radiation-induced sarcomas are an infrequent but well-recognized complication of radiation therapy. Other chest wall injuries due to radiation therapy are osteochondroma and rib or clavicle fractures. Knowledge of the imaging features of injuries caused by radiation therapy can prevent misinterpretation as recurrent tumor and may facilitate further treatment.