The clinical and pathologic findings of 11 infiltrating syringomatous adenomas of the nipple (ISA) were studied. All neoplasms were composed of small ducts and solid strands of epithelial cells surrounded by desmoplastic stroma. Ten of the 11 invaded the smooth muscle of the nipple, four extended to underlying breast tissue, and one showed perineural invasion. All lesions had an infiltrative margin, but 10 were treated successfully by local excision, even though five (45%) recurred. None metastasized. ISA must be distinguished from nipple duct adenoma and tubular carcinoma. Its clinical significance lies primarily in its recognition as a distinctive benign neoplasm. In the past, a variety of terms have been used to describe this lesion, whether it occurred in the skin, nipple, or substance of the breast. "Infiltrating syringomatous adenoma" is the preferred term to avoid using "carcinoma" for lesions involving the breast.