A prospective study of the immediate complications of 370 consecutive breast-imaging procedures (203 wire localizations and 167 radiographically or sonographically guided fine-needle aspirations) is reported. Vasovagal reactions occurred in 27 (7%) of 370 cases, ranging in severity from syncope (four of 370, 1%) to mild light-headedness. These vasovagal reactions were independent of procedure type or use of local anesthesia, but were more common in younger patients. Other complications included prolonged (5 min or longer) bleeding (three of 370, 1%) and extreme pain (two of 370, 1%). One patient was found to have malignant hypertension. We conclude that wire localizations and imaging-guided aspirations are generally well tolerated procedures. However, vasovagal reactions are frequent enough to warrant close observation of patients. Radiologists and breast-imaging personnel should be able to recognize and treat vasovagal reactions.