SUMMARYThe aim of this study is to demonstrate the spectrum of mammographic appearances of mammary duct ectasia that mimic carcinoma in a breast cancer screening programme. Between February 1989 and March 1993, 40 003 women underwent screening mammography as part of the Western Australia Women's Cancer Prevention Unit screening programme. Fine needle aspiration or excisional biopsy was performed on 1437 women, and 12 cases of cytologically or histologically confirmed mammary duct ectasia were detected. A total of 14 mammographic abnormalities from 12 asymptomatic female patients were biopsied, and confirmed to represent mammary duct ectasia. The mammographic spectrum included eight areas of microcalcification (two of which were extensive), three spiculated masses and three lobulated, partially smooth masses. Five of these women showed no other mammographic stigmata of mammary duct ectasia in either breast. Additional features of mammary duct ectasia, including nipple retraction, retro‐areolar duct dilatation or macrocalcification were identified in seven women. Mammographic features of mammary duct ectasia are frequently detected in asymptomatic women undergoing screening mammography and cause no diagnostic dilemma. Occasionally mammary duct ectasia will have a mammographic appearance that is indistinguishable from carcinoma, necessitating breast biospy. In this study 40% of those women with mammary duct ectasia that were submitted for biopsy had no other feature of mammary duct ectasia that could have suggested the pre‐operative diagno