Sezary syndrome is a variant of cutaneous T-cell lymphoma and likely represents the leukemic phase of mycosis fungoides. Sezary syndrome is characterized by generalized erythroderma, pruritus, generalized lymphadenopathy, and circulating atypical cells with cerebriform nuclei. Histopathological features are variable, as this is a later stage in the development of mycosis fungoides. Atypical lymphocytes in the dermis and Pautrier`s microabscesses may be present on a histopathological examination but up to one-third of cases may have non-specific findings. Immunological findings supporting a diagnosis of Sezary syndrome include a predominance of CD4+ lymphocytes in both skin biopsy specimens and peripheral blood. In our case, a 48-year-old male was referred for evaluation of generalized hyperpigmentation with exfoliation on his entire body. We suspected that the clinical features represented Sezary syndrome. We obtained a lymph node biopsy, immunological cell typing, and a peripheral blood smear and diagnosed Sezary syndrome. (Korean J Dermatol 2011;49(12):1131~1134)