The features of ductal adenoma of the breast, a solid intraductal tumor, include the following: arrays of long, straight, narrow, roughly parallel tubules composed of distinct epithelial and myoepithelial cells; a modest amount of fibrous tissue that separates the ducts from one another; and a fibrous capsule. We found this neoplasm in four women (ages 27 through 61 years) who had the complex of myxomas, spotty pigmentation, endocrine overactivity, and schwannomas, an autosomal dominant familial syndrome. The lesion was bilateral in two of the women. Each of the patients had mammary myxoid mesenchymal lesions typical of the complex. Two tumors were symptomatic (bloody nipple discharge); the four others were not. Five of the six tumors formed palpable masses that were located close to the areola. The mammograms suggested carcinoma. On microscopic examination, four of the six adenomas were mistaken for carcinoma; none recurred or metastasized. Circumstantial evidence suggests that the ductal adenoma of the breast is a component of the complex of myxomas, spotty pigmentation, endocrine overactivity, and schwannomas.