To assess the value of routine ultrasound-guided fine needle aspiration (US-FNA) of solid mass lesions of the breast, all such patients presenting to the breast clinic over a 5 month period were offered US-FNA in addition to standard imaging. One thousand, three hundred and eight-six consecutive patients were assessed and 77 solid mass lesions identified. US-FNA was performed in 49 of these. Sixteen demonstrated cytological features of malignancy that was confirmed at surgery. US-FNA did not diagnose malignancy in cases with typical benign imaging features. It did alter diagnosis from an equivocal suspicious mass lesion to a definite diagnosis of malignancy in four cases (25%). It also altered diagnosis from an equivocal, probably benign, diagnosis to a more confident diagnosis of benign disease in 18 (58%) of benign cases. US-FNA confirmed the diagnosis of malignancy in four cases where a suspicious mass could only be imaged by ultrasound. US-FNA is simple, rapid and, unlike large Tru-Cut biopsies, is not associated with complications. It causes only minimal discomfort to both patient and operator. We recommend that US-FNA becomes a routine component of the imaging workup of breast mass lesions both to exclude malignancy in equivocal cases and to confirm malignancy when this is expected.