This paper summarizes our clinical experience with 165 cases of biopsy-proved mycosis fungoides. In 34% of the 106 deceased patients there was a transition from mycosis fungoides to reticulum cell sarcoma (14 cases), to lym-phosarcoma (15 cases), or to Hodgklrfs disease (7 cases). Five of the 14 patients with reticulum cell sarcoma had terminal monocytlc leukemia, and 6 of the 15 with lymphosarcoma had terminal lympho-blastic leukemia. In 23 of the 42 patients autopsied the disease remained as mycosis fungoides throughout its course. The pleomorphic infiltrate without Sternberg-Reed cells involved the lymph nodes in 4 and the viscera in 9 of the patients autopsied. No findings in the blood or marrow could be considered as pathognomonic of mycosis fungoides except perhaps an absolute lymphopenia noted in 76% of the patients. Total body surface electron beam therapy is the most effective and practical form of palliative therapy. Skin tolerance is the only limiting factor; bone marrow is not significantly affected.