Mycosis fungoides is an uncommon, chronic fatal disease of lymphoreticular system associated with primary ski3 involvement for many years and terminating as a malignant lymphoma with involvement of lymph nodes and viscerae. On occasion it simulates numerous other nonspecific benign skin lesions, thus it may be impossible to decide whether the infiltrate represents early mycosis fungoides or nonspecific on the histopathologic ground alone. A case of mycosis fungoides was confirmed by electron microscopy and reported here. The patient was 69-years-old male who had suffered from erythematous scaly eruption on the whole body since 10 years. Skin biopsies of 4 times showed focal ulceration with chronic nonspecific inflammation and polymorphic cell infiltration in lower dermis, thus possibility of mycosis fungoides could not be completely ruled out. Electron microscopically several atypical lymphoid cells, which had a large cerebriform nucleus with peripheral condensation of dense chromatin and scant cytoplasm, were noted in the upper dermis. Intraepidermal infiltration of these atypical cells was also seen. It was thought that the electron microscopic study may be very helpful to differentiate equivocal mycosis fungoides from the nonspecific dermatosis.