The aim of this study was to evaluate the expression of GCDFP15 and GATA-binding protein 3 (GATA-3) in extramammary Paget's disease (EMPD) skin and serum samples and to assess their availability as tumor markers for the diagnosis and assessment of disease severity in primary EMPD. By immunohistochemistry, the expression of GCDFP15 and GATA3 was examined in skin specimens. There was no correlation between serum levels of GCDFP15 or GATA-3 and the disease stage. Our results indicate that GCDFP15 and GATA-3 are useful for the diag- nosis of primary EMPD, but not for monitoring disease progression, and suggest that GATA-3 is a more reliable marker than GCDFP15 for the diagnosis of primary EMPD.