Perianal Paget's disease is rare. It usually represents intraepidermal extension of an invasive carcinoma from an adjacent internal organ, but some cases represent primary intraepithelial cutaneous apocrine adenocarcinomas. Here, we report a unique case, which we interpret as synchronous primary perianal Paget's disease and lower rectal adenocarcinoma. Immunohistochemical stains demonstrated that the Paget's cells were CK7+/ CK20-/GCDFP+, whereas the rectal adenocarcinoma was CK7+(variable)/CK20+/GCDFP-. This discordant immunoprofile supported our impression that the Paget's disease in this patient was of cutaneous apocrine origin rather than a pagetoid extension from the patient's nearby rectal adenocarcinoma-to our knowledge a hitherto undocumented occurrence.