To determine useful immunohistochemical markers for tumor cells in extramammary Paget's disease (EMPD), immunohistochemical (IHC) examinations in 17 patients with EMPD, including 4 patients with dermal invasion, were performed. Among the antibodies examined, cytokeratin 7 (CK7) and CK19 were strongly positive for both intraepidermal and dermally invasive tumor cells in all patients. CAM5.2 and mucin 1 (MUC1) were also good markers. Although IHC examination revealed positive for HER-2 in 4 EMPD patients with dermal invasion, 4 out of 13 noninvasive patients were IHC negative. Fluorescence in situ hybridization (FISH) study revealed negative results for HER-2 gene amplification in 8 IHC positive patients, including each 4 patients of both noninvasive and dermal invasive cases. Our results show that besides CK7, CK19 is another favorable marker of tumor cells of EMPD. Four patients with dermal invasion were strongly positive for HER-2, although negative results were obtained in the FISH study. Further investigations are required to confirm the results of the FISH study.