BACKGROUND One of the more frustrating complications after breast biopsy with needle localization is a missed lesion. To reduce the number of missed lesions, radiographs of the surgical specimen are usually obtained. In this study we determined the accuracy of specimen x-ray, the incidence of missed lesions, and the management of patients with this complication. METHODS The result of specimen x-ray was compared with that of a postoperative mammogram in 192 patients who underwent breast biopsy with needle localization. The incidence of missed lesions was also determined from postoperative mammogram, and the management of patients with this complication was analyzed. RESULTS The incidence of false-positive specimen x-ray was 7.8% and that of false-negative 55%. The sensitivity, specificity, and accuracy of specimen x-ray were 96%, 28%, and 89%, respectively. The incidence of missed lesions was 3.2% and of incompletely excised lesions 6.4%. Eighteen of 24 patients with a missed or incompletely excised lesion were treated expectantly because postoperative mammogram showed the lesion to be stable. None of these patients has required a subsequent biopsy. CONCLUSIONS Specimen x-ray can be false positive or false negative. An important implication of this finding is that a postoperative mammography should always be performed after biopsy with needle localization, regardless of the result of the specimen x-ray, to make certain the lesion has not been missed.