We treated a case of extramammary Paget's disease that affected the scalp of a 45-year-old female. It is extremely rare that the disease arises in areas other than the anogenital region and the axillae. The lesion was a round erythematous oozing crusted hairless patch. Histopathologically, many pagetoid cells were found within the epidermis and dermis. The cytoplasms of these cells stained with alcian blue at pH 2.5, CEA, EMA and low-molecular-weight-cytokeratin. The patient underwent a wide local excision. We used a mapping technique to reveal the distribution of microscopically involved lesions.