High frequency ultrasonography has become the standard for guiding needle biopsy in cases of breast masses, whether a fine needle or a core biopsy is used and guiding the drainage of cysts and abscesses. US has also become the preferred method for guiding insertion of various localization devices for non palpable masses. Recently, US has been used to monitor the placement of percutanous ablation devices, such as radiofrequency ablation needle electrodes into breast masses including carcinomas.