Sonography is unable to replace x-ray mammography in the detection of early-stage clinically occult breast cancer. Despite its inability to differentiate solid benign from malignant masses sufficiently well to avoid biopsy, an important adjunctive role has been defined. Sonography can be used to guide the aspiration of cysts that could not be drained clinically and in so doing obviate surgery to remove these lesions. In addition, in selected patients it can guide the placement of wire guides for the surgical removal of clinically occult lesions. The results of 43 sonographically guided interventional procedures in the breast are discussed. In 35 of 38 sonographically guided cyst aspirations, fluid was obtained, including 11 patients in whom there had been unsuccessful clinical attempts. In five additional patients with indeterminate solid lesions and negative aspirations, sonography was successfully used for preoperative wire placement.