Needle aspiration of a breast mass, a procedure widely employed in Scandinavia but neglected in the United States, has an important role in the diagnosis of carcinoma of the breast. Five hundred and ninety-seven patients had aspirations from 706 lesions, 415 solid and 291 cystic. There were 83 malignancies, with abnormal cells in 73. In the majority the diagnosis could be made readily. There is no known contraindication to the procedure. Aspiration at the initial visit may alert the physician to malignancy, thus avoiding undue delay in treatment.