Paget's disease may occur at mammary and extramammary sites. Mammary Paget's disease typically involves the nipple and adjacent skin. Almost all such cases are associated with an underlying ductal carcinoma of the breast. A case of Paget's disease occurring at the site of an ectopic breast adjacent to a supernumerary nipple and associated with an underlying intraductal carcinoma is described. A search of the literature revealed no previous report of such cases. Detailed clinical history and histopathologic, histochemical, and follow-up information on this case are presented. The literature on mammary and extramammary Paget's disease is reviewed.