Microcalcifications constitute an important part of nonpalpable breast lesions and may be the first sign of a breast carcinoma. Between 1975 and 1984, 150 consecutive patients with clusters of at least five microcalcifications without palpable findings as the only indication for biopsy were treated. One hundred seventy-three groups of microcalcifications were excised and 51 malignancies were detected (29.5%). Most of the malignant lesions were noninfiltrating (56%). Axillary or distant metastases occurred in 11% of the fully evaluable cases. This warrants the expectation that these patients have a very favorable prognosis. Breast biopsy for nonpalpable-clustered microcalcifications is a feasible and valuable procedure. Close cooperation is required between the surgeon, radiologist, and pathologist.