A case of clone-negative Sézary syndrome is reported. The patient was a 69-year-old male and showed the classical trias of Sézary syndrome, that is erythrodermia, generalized lymphadenopathy and neoplastic T-cells in skin, lymph nodes and peripheral blood. There is at present no consensus on the diagnostic criteria of Sézary syndrome, if T-cell clonality is not detected in peripheral blood with Southern blotting. The EORTC group demonstrates T-cell clonality is getting major as a diagnostic criterion of Sézary syndrome, which is generally accepted. However, we suppose such cases like ours are present, and should be called clone-negative or nonclonal Sézary syndrome. In addition, we have to carefully observe whether these cases advance to real Sézary syndrome with T-cell clonality, though these cases are not naturally included into cutaneous T-cell lymphomas. [Skin Cancer (Japan) 2004; 19: 128-131]
