Paget's disease is an intra-epidermal adenocarcinoma seen over the nipple/areola (mammary Paget's disease) or in extramammary body zones, such as the anogenital and perineal skin and the axilla. Mammary and extramammary Paget's disease share many common clinicopathological features but also show several differences, namely, with regard to pathogenesis and association with underlying malignancies. Indeed, mammary Paget's disease is as a rule associated with an underlying breast carcinoma whereas association of extramammary Paget's disease with underlying (skin or visceral) malignancies occurs much less frequently. We review here the main clinicopathological and therapeutic features of mammary and extramammary Paget's disease.