Mammary duct ectasia developed in three postmenopausal patients who had had pituitary chromophobe adenomas. The first patient had bilateral duct ectasia that developed 8 and 11 years after hypophysectomy. The second patient, who also had bilateral ectasia, had a prolactin-producing pituitary adenoma for which bromocriptine was prescribed. The ectasia developed in one breast before commencing bromocriptine therapy, and in the other breast 2 years later. The third patient also had a prolactin-producing pituitary adenoma. Unilateral duct ectasia developed while bromocriptine was taken. The ectasia in all patients was very marked and affected all excised ducts. Cholesterol granulomas were sometimes very extensive. These cases suggest a relationship between certain hypothalamic/pituitary disorders, possibly related to prolactin secretion and the development of mammary duct ectasia in postmenopausal patients.