Sezary syndrome is an aggressive, leukemic cutaneous T-cell lymphoma variant, characterized by a triad of circulating neoplastic T cells and erythroderma with/without associated lymphadenopathy. A 51-year-old man presented with erythroderma and multiple nodular skin lesions over the face. The facial skin was thickened, producing “leonine facial” appearance. On physical examination, the axillary and inguinal lymph nodes were enlarged. Investigations revealed the presence of atypical lymphoid cells in the peripheral blood, bone marrow, and skin. The histopathology of skin showed dermal infiltration of atypical small lymphocytes with mild epidermotropism. Immunohistochemical studies showed that the infiltrated cells were positive for CD3 and CD4, but negative for CD8 and CD20. A diagnosis of Sezary syndrome was made based on the clinical, peripheral blood, and immunophenotypical findings. (Korean J Dermatol 2020;58(1):43∼46)