the invention is directed biopsy site markers and methods of marking a biopsy site , so that the location of the biopsy cavity is readily visible by conventional imaging methods , particularly by ultrasonic imaging . the biopsy site markers of the invention have high ultrasound reflectivity , presenting a substantial acoustic signature from a small marker , so as to avoid obscuring diagnostic tissue features in subsequent imaging studies , and can be readily distinguished from biological features . the several disclosed embodiments of the biopsy site marker of the invention have a high contrast of acoustic impedance as placed in a tissue site , so as to efficiently reflect and scatter ultrasonic energy , and preferably include gas - filled internal pores . the markers may have a non - uniform surface contour to enhance the acoustic signature . the markers have a characteristic form which is recognizably artificial during medical imaging . the biopsy site marker may be accurately fixed to the biopsy site so as to resist migration from the biopsy cavity when a placement instrument is withdrawn , and when the marked tissue is subsequently moved or manipulated .