Review of the results of 100 consecutive aspiration breast biopsies disclosed that this technique failed to identify 11 of the 33 breast cancers in the series; however, it identified 3 breast cancers that were not recognized by clinical examination. In one patient who had a fibroadenoma, suspicious cells were seen in the material sent for cytologic examination. It is concluded that a negative aspiration biopsy does not contraindicate tissue biopsy when the clinical findings suggest cancer. Aspiration biopsy can uncover clinically unsuspected cancers. When the lesion appears to be malignant on a clinical basis, aspiration biopsy can obviate formal biopsy. In this way time is saved for all those involved and the fashioning of the mastectomy flaps is facilitated.