One year after the birth of her second child, the patient visited the clinic, concerned that “my moles have changed a little.” The patient was breastfeeding her infant daughter at this time. Clinical examination revealed 3 focal areas of darkening in the large garment nevus of the patient on the lateral part of her right thigh (lesion 5 in the Figure, C), right inguinal crease (lesion 6, not shown), and medial part of her right thigh (lesion 7 in the Figure, C). There was also continued lightening in several satellite nevi, particularly on the lower parts of her legs. Biopsy samples from these 3 lesions, along with a fourth sample (2 cm medial to lesion 5 in the Figure, C) of a nearby stable satellite nevus for comparative purposes, are shown in circles in the Figure, C. None of the nevi biopsied showed cytologic atypia, whether during pregnancy or post partum. Immunohistochemical staining for ERβ revealed increased nuclear staining compared with the biopsy samples taken while pregnant, with dermal nuclear staining averaging 2.67 of a total staining score of 5. In addition, cytoplasmic staining, which was not observed in the biopsy samples during pregnancy, was seen in these samples, which averaged a staining score of 0.67 of 5 (Figure, F and G).7,11 At recent follow-up visits, while neither pregnant (20 months post partum) nor breastfeeding, the patient had continued to notice areas of darkening in her garment nevus and satellite nevi on the arms, although some of the satellite nevi on the legs remain less pigmented.