The difficulties created by the lack of generally accepted views on classification, diagnostic criteria and natural history of the cutaneous lymphomata are discussed. Only the lymphomata which remain confined to the skin throughout the major part of their development are considered. It is emphasized that these are extremely radiosensitive and that there must be some factors as yet unknown which play a part in their unique natural history and response to treatment. The cutaneous lymphomata are considered under three headings: (1) lymphocytoma, (2) lymphosarcoma and reticulum cell sarcoma, (3) mycosis fungoides. The characteristics of the first two are discussed briefly and illustrative examples are given. The relatively benign nature of the lymphocytoma is stressed. It is suggested that the solitary lymphosarcoma of the skin should be treated by radical radiotherapy since long-term survival or cure may be achieved. The treatment of mycosis fungoides is considered in greater detail. The physical advantages of electron therapy are described and details given of whole body surface treatment with electrons produced by a 6 MeV linear accelerator and slowed down with carbon decelerators of appropriate thickness. The results in 73 patients treated by electrons are analysed. The early and late side-effects are mentioned and the necessity for investigating other forms of treatment is stressed. It is concluded that at the present time electron therapy is the most satisfactory form of treatment for mycosis fungoides.