High-resolution, high frequency, three-dimensional (3D) breast ultrasound can be used as the first-line, noninvasive imaging tool for the evaluation of patients with breast discharge. From June 2000 to April 2001, the medical records of 27 consecutive patients with pathologic nipple discharge were evaluated using 3D breast ultrasound equipped with automatic volume scan. Four patients did not undergo surgery because only mild duct dilation, without any visible tumor or vessel structures (around the dilated duct), was found on sonography. Of the remaining 23 patients who subsequently had surgery, four had watery discharge, seven had bloody discharge, five had serous discharge and seven had serosanguineous discharge. The final diagnoses were based on determinate histopathology from surgical specimens: intraductal papillary carcinoma (one), intraductal papillomatosis (five), and intraductal papilloma (17). In one of the four patients who did not have surgery, the bloody discharge disappeared 2 months later without recurrence during subsequent follow-up. The availability of high-frequency linear transducers now enables us to visualize the mammary duct in detail. The 3D volume images can be reviewed immediately in the bedside ultrasound machine or retrospectively in the computer, so that the relationships between nipple, duct and tumor can be clearly identified. This advantage is one that conventional 2D ultrasound cannot provide.