Radiotherapy causes changes in a treated malignancy and the surrounding normal tissue which must be included in the radiation fields. Awareness of the expected appearance of these changes frequently permits differentiation of them from superimposed infection, recurrent malignancy, radiation-induced tumors, and the other true complications of radiation therapy. Radiotherapy changes are a function of the tissue volume treated, field shape, total dose and how it was delivered, time from completion of therapy, and the possible effect of other therapies. Timing of radiation changes varies in the different organs. Acute radiation pneumonitis is generally seen approximately 2 months after completion of radiotherapy, but radiation pericarditis not until 6-9 months after therapy. Radiation-induced sarcomas do not develop on average until 10-15 years after radiation therapy. An overview of expected findings and complications in the lungs, heart, gastrointestinal tract, genitourinary tract, and bones is presented.