e18511 Background: Mycosis fungoides (MF) and Sezary's syndrome are the most common subgroup of cutaneous T-cell lymphoma. Total or partial skin electron beam irradiation (TSEI, PSEI) is an accepted treatment option in cases of disease that is limited to the skin and as palliative treatment in advanced disease. Consequently, long term follow-up of these patients and detection of secondary malignancies after TSEI/PSEI is crucial. The aim of this study was to summarize long term follow-up of MF patients treated by TSEI or PSEI and to evaluate the rates of secondary malignancies. Methods: A retrospective review of the medical charts of all consecutive patients diagnosed with MF who was treated from January 1960 to June 2010 at our hospital was conducted. Data collected included demographics, date of diagnosis, staging, treatment, and secondary malignancies. Results: One hundred ninety six patients were included (132 M, 64 F). The median age at diagnosis was 67.3 years. The mean follow-up was 109.4±89.4 months (range 1-566). One hundred patients received TSEI, 45 patients received PSEI, and one patient was treated by low dose total body photon irradiation combined with TSEI. Fifty patients (50/196, 25.5%) developed a second malignancy, 16 patients (16/196, 8%) had a third malignancy, and 4 (2%) patients developed a fourth malignancy. Conclusions: MF is associated with development of sequential malignancies. The contribution of TSEI or PSEI to the development of secondary malignancies is yet to be determined. Long term follow-up in this group of patients is essential.