A 54-year-old woman was noted to have a new mass on screening mammography. (A) Close-up of mediolateral oblique (MLO) mammogram shows lobulated, circumscribed mass (arrow). (B, C) Targeted ultrasonography shows lobulated simple cyst corresponding to the mammographic abnormality, a benign finding. Apparent thin septation in image (C)(arrow) is due to lobulation of the cyst. (Courtesy of Wendie A. Berg, MD, PhD, Lutherville, MD.)