Radiation therapy is an important technique for treating cancer. In the evaluation of the results of radiation therapy with computed tomography (CT), radiation-induced injuries to normal tissues are often detected. Common complications include pneumonitis, calcified lymph nodes, gastric ulceration, enteritis, hepatitis, cystitis, nephritis, osteitis, and insufficiency fractures. Rare complications include spontaneous pneumothorax, thymic cysts, vascular calcifications, and osseous sarcomas. Radiation-induced injury can usually be diagnosed from characteristic CT appearances and knowledge of the radiation port, radiation dose, and time interval since therapy. CT findings that cannot be explained on the basis of radiation therapy or that are suggestive of recurrent disease must be further evaluated.