In order to evaluate the level of cell differentiation in extramammary Paget's disease (EMPD) and the relation with prognosis, the pathologic morphology of 20 EMPD cases were reviewed. We found two marked features of the invasive and metastatic Paget's cells: first, the Pagat cells were usually of signet ring shape; second, the cells formed gland-like structures. These features can be regarded as low differentiation and important risk factors for invasion and metastasis in EMPD.