Our laboratory previously conducted feasibility studies of autonomousrobotic breast biopsy guided by 4D ultrasound. Using a complete 3D image volume,processed by elementary thresholding algorithms with no human intervention, therobot was able to successfully target bright voxels representingmicro-calcifications and dark regions representing cysts in turkey breasttissue. We now describe a clinical prototype of a computer-controlled single armrobot guided by 4D ultrasound which can autonomously locate a breast lesion andthen fire a spring-loaded biopsy needle into the lesion. RMS error in a watertank experiment locating a bright point target was 2.82 mm. © 2010 IEEE.