Between 1966 and 1981, 20 patients (191 lesions) underwent palliative radiation therapy for control of biopsy-proven cutaneous mycosis fungoides. Six patients (47 lesions) and an additional 34 lesions from the remaining 14 patients with complete response to treatment were excluded from the study because of follow-up of less than one year. Included in the remaining 110 lesions were all recurrences and all partial responses. The modalities for treatment included superficial X rays, Cobalt-60 or electron beam irradiation. The total tumor doses employed ranged from 600-4000 cGy. The 110 lesions (14 patients) were retrospectively analyzed to determine the dose required for local control of the lesions. Fifty-three percent of the lesions were classified as plaques, 20% as tumors less than or equal to 3 cm in diameter, and 27% as tumors greater than 3 cm in diameter. Complete response to treatment was observed in 95% of the plaque lesions, 95% of the tumors less than or equal to 3 cm in diameter and 93% of tumor greater than 3 cm in diameter. A complete response to treatment was noted in all lesions receiving greater than 2000 cGy. In the total population of lesions having a complete response, a local infield recurrence rate of 42% was noted in the group receiving less than or equal to 1000 cGy, 32% in those receiving 1001-2000 cGy, 21% in those receiving 2001-3000 cGy, and 0% in the group receiving greater than 3000 cGy. No infield recurrence was seen when the treated lesion received a total tumor dose greater than or equal to TDF of 49. Of those lesions which recurred, the mean time to recurrence for the first three dose ranges above were 5 months, 10 months and 16 months respectively. Eighty-three percent of the 30 recurrences were seen within one year of treatment; 100% of the recurrences occurred within two years of treatment. The data from this study indicate that tumor doses equivalent to at least 3000 cGy at 200 cGy per fraction, five fractions per week (TDF greater than or equal to 49) are needed for adequate local control of cutaneous mycosis fungoides lesions.