Mammary carcinoma arising in ectopic breast tissue is an uncommon occurrence. Most reported cases have involved ductal carcinoma, but other types, such as medullary, papillary, and lobular carcinomas, have been described. For pathologists, the diagnosis of mammary carcinoma arising in ectopic breast tissue can be difficult, especially in the axilla, where carcinoma of adnexal origin must be excluded. We describe a 46-year-old woman who developed invasive (juvenile) secretory carcinoma in ectopic right axillary breast tissue and micrometastatic carcinoma in an ipsilateral axillary lymph node. The carcinoma arose in a right axillary mass that had been present for 8 years, from which she had secreted fluid during prior breast-feeding. To our knowledge, this is the first report of secretory carcinoma arising in axillary breast tissue to be documented in the current literature.