The substantial majority of questionable lesions detected by mammography are benign, and there is growing interest among health care professionals and patients in alternatives to surgical biopsy for diagnosing these lesions. Stereotactic breast biopsy is an x-ray guided method for localizing and sampling breast lesions discovered on mammography and considered to be suspicious for malignancy. Its use in sampling small, nonpalpable breast lesions has been investigated over the past 15 years, using fine-needle aspiration for cytology and, more recently, core-needle biopsy for histology. Multiple series comparing stereotactic biopsy with surgical biopsy have shown that stereotactic techniques accurately sample small lesions and have a sensitivity of 90 to 95 percent for breast cancer detection. State-of-the-art stereotactic breast biopsy is comparable in sensitivity to surgical biopsy, and the procedure is quicker, cheaper, and easier than the standard practice of preoperative, mammographically guided localization followed by surgical biopsy. In an age of miniaturization, stereotactic techniques provide miniature breast biopsies. The University of Chicago acquired the first prone stereotactic table in the United States in 1986, and we have found stereotactic breast biopsy to be a very good alternative for certain lesions that would otherwise require surgical biopsy for diagnosis. Most lesions (70 percent) sent to conventional biopsy at the University of Chicago between 1986 and 1989 were graded by observers as being in a low-suspicion category (less than 10 percent chance of malignancy based on mammographic findings), and the positive malignancy yield of this category of lesions was seven percent. These lesions were also examined with stereotactic fine-needle aspiration performed as a "piggy-back" procedure to the needle localization for surgery. The results of this study have led us to use stereotactic biopsy rather than surgical biopsy for low-suspicion lesions since then. We currently use stereotactic breast biopsy for about half the nonpalpable lesions considered for breast biopsy at our institution and find it to be reliable and readily accepted by informed patients. The introduction of automated core-biopsy guns has escalated interest in the technique, due to increased confidence in the histologic samples obtained and the ability to make specific benign diagnoses more frequently. Some centers have extended the potential use of stereotaxis to virtually all suspicious mammographic lesions, including those with a high probability of malignancy, to plan definitive surgery. Based on current estimates, there are now over 1,000 centers either investigating or using stereotactic biopsy for occult breast lesions.