Mycosis Fungoides (MF) is typically characterized by a mature CD4+ memory T-cell phenotype, and regarded as a helper T-cell (Th)2-skewed disease. Here, using skin samples from MF (n=21), healthy volunteers (n=17), atopic dermatitis (n=17), and psoriasis (n=9), we performed RT-PCR to show highest interleukin (IL)-32 mRNA expression in MF compared to benign inflammatory diseases, and its increasing expression with disease progression. By immunohistochemistry and immunofluorescence, we confirmed IL-32 protein expression by numerous CD3+CD4+ T-cells and some epidermotropic T-cells in MF lesions. IL-32 is expressed by MyLa cells (MF cell line) and promoted their proliferation and viability in a dose-dependent fashion. IL-32-treated MyLa and HH cells (CTCL cell line) showed upregulation of cell proliferation and survival genes. Of major 'polar' T-cell cytokines, only IFN- mRNA increases with MF progression and positively correlates with IL-32 mRNA expression levels. Th2 cytokines do not show consistent increases with MF progression nor positive correlation with IL-32 mRNA expression levels. Furthermore, by flow cytometry, IL-32 production by circulating activated T-cells in healthy individulas was found in IFN-+ and IFN-- cells but not in IL-4+ or IL-13+ cells. In conclusion, we identified IL-32+ cells as likely tumor cells in MF, and clearly showed that IL-32 mRNA expression levels increase with MF progression. We found that IL-32 mRNA expression levels in MF are significantly higher than those in other skin diseases, and that some IL-32+ T-cells are independent from defined Th subsets. Thus IL-32 may play a unique role in MF progression as an autocrine cytokine.