Pigmented mammary Paget's disease (PMPD) is a rare subtype of mammary Paget's disease. The differential diagnosis of PMPD and melanoma is difficult clinically and sometimes histopathologically. Here we present three cases of PMPD with a variable-sized lesion. All cases showed an irregular-shaped black-brown macule, one of which was accompanied by nipple retraction. Dermoscopically, all cases showed reticular pigmentation with or without irregular black dots, regression structures and streaks, which were indistinguishable from those of melanoma. In all but one of the cases, preoperative examinations confirmed the presence of a subcutaneous mammary lesion. All patients underwent a total mastectomy with the histopathological results indicating invasive ductal carcinoma. These cases emphasize how difficult it is to distinguish PMPD from melanoma. Dermoscopic features also mimic those of melanoma, but the reticular pigmentation seen in all cases could be a feature specific to PMPD. For suspicious cases, histopathological assessment using immunohistochemistry is highly recommended.