Radiation therapy is the most effective single agent for the treatment of mycosis fungoides. There are well-defined dose-response relationships for achieving a complete response as well as the durability of this response. Techniques of electron beam therapy have been developed that permit treatment of the entire skin. Total-skin electron beam therapy is an important form of management, especially for patients who have thick generalized plaque or tumorous disease. Radiation therapy may also be used selectively for treatment of extracutaneous disease.