Pathologically involved ectopic breast tissue is not commonly encountered. There have been, however, intermittent reports of involvement of ectopic breast tissue by many of the same benign and malignant processes that occur in normally located breast tissue. This article records what, to our knowledge, is the first case of cystosarcoma phyllodes arising in ectopic breast tissue of the axillary regions and is the second reported case of three primary cystosarcoma phyllodes arising synchronously. A review of the available literature pertaining to ectopic breast tissue and multiple cystosarcoma phyllodes is also presented.