Angiogenin is a member of the ribonuclease superfamily that is associated with the angiogenic process. Angiogenesis is regarded as an important step to support primary and metastatic tumor growth. In cutaneous T cell lymphoma (CTCL), angiogenesis in lesional skin is increased, suggesting that interaction between tumor cells and their microvasculature are likely to occur during progression of CTCL. Patients with hematological malignancies show increased serum angiogenin levels, which are related with poor overall survival. To investigate possible roles of angiogenin in development of CTCL, we measured serum angiogenin levels in 36 patients with CTCL and 21 healthy controls by enzyme-linked immunosorbent assay. We also investigated angiogenin mRNA and protein expression in lesional skin of CTCL by quantitative RT-PCR and immunohistochemistry. Serum angiogenin levels in patients with CTCL were significantly higher than those in healthy controls. When classified with types of skin lesions, serum angiogenin levels were elevated only in erythrodermic CTCL patients. Angiogenin mRNA expression levels in lesional skin were significantly elevated in erythrodermic CTCL compared to normal skin. Immunohistochemical study revealed that angiogenin was expressed by keratinocytes, endothelial cells, and infiltrating lymphocytes in CTCL. Our results suggest that enhanced angiogenin expression may be related with a poor prognosis of erythrodermic CTCL. As angiogenin acts as an inhibitor of polymorphonuclear leukocyte degranulation, angiogenin may also be linked to impaired host defense in erythrodermic CTCL.