The medical records of 192 women with nonpalpable mammographically detected breast lesions who underwent needle-localized breast biopsy between January 1989 and January 1991 and between March 1992 and March 1994 were reviewed. Of the 192 patients examined, 100 underwent biopsy for evaluation of microcalcifications suggestive of malignancy. Ninety-two biopsies were performed for non-specific radiodensities not inclusive of microcalcifications. This study examines the radiographic characteristics of the nonpalpable breast lesion. Although presence of microcalcifications on mammograms are an important finding in detection of breast carcinoma, it must not be considered pathognomonic. Other distinguishing factors require evaluation to assess the indication for biopsy. Central to this study was the presence of microcalcifications alone or as detected in association with a dominant mass. Cancer was discriminated in 38 (20%) of the patients studied. Mammographic findings with microcalcification, regardless of the presence of a mass, were found to be malignant in 20% of patients undergoing biopsy. Nine percent of biopsies done to evaluate microcalcifications alone were malignant. The finding of microcalcification associated with a dominant mass proved malignant in 34% of patients who had a biopsy done. The authors include guidelines for increasing the effectiveness of needle-localized biopsies of the breast.