Although palpable and mammographic breast masses are common and frequently reflect underlying fibrocystic change, they must be distinguished from breast malignancy. Clinical characterization of these masses is often unreliable, and mammographic appearances alone cannot distinguish between those that are solid and those that are cystic. Sonography is an important adjunct to characterize these abnormalities further. Management of solid masses is well established, but overlap in appearance of cystic lesions has led to variability in reporting and management. With current high-resolution ultrasound, specific observations can accurately characterize most cystic masses, thereby facilitating management decisions.