High-dose irradiation is an effective treatment for tumors in the head and neck. Radiation-induced complications are uncommon but may result in chronic, progressive symptoms months or years after therapy. In 19 (1%) of 1,950 patients who underwent successful high-dose irradiation of head and neck tumors over a 5-year period, delayed radiation-induced changes were documented with imaging. These changes can be categorized as soft-tissue, bone, and cartilage necrosis; fibrosis leading to functional disorders; arteriopathy; central nervous system reactions, delayed myelopathy, and cranial nerve palsies; and the development of meningiomas. Radiologic features of radiation-induced soft-tissue, bone, and cartilage necrosis include inflammatory swelling adjacent to the area of involvement; deep gas-containing ulcerations; sclerotic appearance of the involved cartilages; fragmentation and sloughing of necrotic bone or cartilage; and abscess and fistula formation. Masticator muscle fibrosis appears as an area of diffusely increased signal intensity on T2-weighted images and of enhancement on postcontrast T1-weighted images. Radiation arteriopathy may manifest as occlusion, subocclusive sclerotic or atheromatous plaque, localized mural thrombus, aneurysm, or, rarely, spontaneous rupture. In central nervous system reactions, imaging findings include demyelination foci in the white matter, focal radiation necrosis, and severe brain atrophy. Radiation-induced meningiomas display the same imaging features as non-radiation-induced meningiomas at computed tomography, magnetic resonance imaging, and angiography, although follow-up examinations may reveal their more aggressive biologic behavior. Knowledge of the radiologic appearance of radiation-induced changes may prevent misinterpretations and facilitate treatment.