The clinical course and management of 85 cases of mycosis fungoides presenting over a 20-year period are described. The extent of skin involvement and presence of lymphadenopathy were seen to be important prognostic factors. The following survival patterns were observed. In eight cases with limited plaque disease there was prolonged disease-free survival after treatment with kilovoltage X-rays; after a median follow-up of 64 months there was only one case of progression to generalized disease. In 49 cases of generalized skin disease (plaque disease +/- tumours; erythroderma) treated with total skin electron beam therapy there was a 24% 5-year disease-free survival; this potential for long-term survival was seen in cases with generalized plaque disease without lymphadenopathy. The remainder of the cases showed a continuously relapsing course. The extent of skin involvement and presence of lymphadenopathy can both be used as known prognostic factors to adopt a logical plan of treatment.