We present the case of a 33-year-old female who developed a cystic nodule on the vulva during pregnancy. Immediately following Cesarean section, the lesion was biopsied and histologic examination revealed a dermal tumor composed of glandular structures arranged in a labyrinth pattern. The glandular structures displayed cytoplasmic vacuolization, large atypical nuclei, prominent nucleoli and scattered eosinophilic luminal secretions. Immunohistochemistry showed the tumor cells to be diffusely positive for CK7 and progesterone receptor with focal expression of mammaglobin and GCDFP-15. The tumor cells were negative for estrogen receptor and CK20. These histologic and immunophenotypic findings were consistent with hidradenoma papilliferum. Our unusual (and to our knowledge first reported) case demonstrates hidradenoma papilliferum in association with pregnancy and raises the possibility of cytologic atypia and lactational change being secondary to hormonal changes in pregnancy.