Breast ultrasonography (US) is not only useful in identifying the cystic content of breast masses but also in characterization of the solid masses. BI-RADS US lexicon, like the mammography lexicon, provides a standard terminology and assessment for breast US reports. In this article, the author examines the different types of cysts and solid lesions and examines how they should be treated. He focuses on categories 2 through 6 of the BI-RADS ultrasonography final assessment categories in American College of Radiology Imaging Network 6666 protocol, which indicate how and if cysts and lesions should be treated by biopsy or aspiration.