Mycosis fungoid (MF) is a non-Hodgkin's T-cell lymphoma determined by primary cutaneous involvement. It is a slow-progressing chronic indolent disease characterized by atypical T-cells with a cerebral nucleus. Management of this disease depends on the stage and is based essentially on the systemic treatment. Radiotherapy intervenes in case of localized or extended tumor, indeed, the radiosensibility of this tumor, like any other hematological affection, makes it possible to obtain a high rate of response. Clinical case: we report the observation of a 46-year-old patient followed since 2012 for mycosis fungoid revealed by a papullo-squamous lesion located at the level of the right lumbar fossa. The diagnosis was confirmed by cutaneous biopsy, showing the presence of T lymphocytes expressing CD2, CD3, CD4, CCR4, CD45RO markers. Initial assessment included a thoraco-abdominal pelvic CT, which was normal, an accelerated sedimentation rate at the 1st hour, a high C reactive protein (CRP), the electrolytic, renal, hepatic status and the hemogram were normal. Patient received 6 courses of chemotherapy according to the COPP protocol with a decrease in the size of the lesion estimated at 40%. A norm fractionated radiation therapy was delivered at the dose of 36Gy. The evolution was marked by a complete remission, maintained after 6 months of the treatment. Mycosis fungoid is a rare disease, whose management must be discussed in a multidisciplinary team. Radiotherapy remains an interesting option for all stages, but has to be validated in largest studies.