Ultrasound of the breast has a role both as the primary and as an ancillary modality in the work-up of breast abnormalities. Its main role is to differentiate cystic from solid abnormalities and to thereby guide further work-up and intervention. Only the diagnosis of a simple cyst will obviate the need for further evaluation or therapy. Doppler ultrasonography of breast lesions may give further information in the future, although this is currently not employed in clinical practice. Various types of ultrasound examinations may yield useful information in the patient with breast cancer or in women with breast prostheses.