Asymmetric breast tissue can nearly always be distinguished from a true mass by means of mammographic evaluation. Stellate masses from early invasive breast cancer are often extremely subtle so that optimal technique and meticulous interpretation are essential. Benign stellate masses such as post-biopsy scarring and fat necrosis frequently have a characteristic appearance. A radial scar is usually indistinguishable from malignancy on the mammogram. Nearly all circumscribed masses are benign and are usually cysts, fibroadenomas, or intramammary lymph nodes. A few circumscribed masses represent in situ or invasive carcinoma or both. Characteristics that may allow a definitively benign diagnosis for a circumscribed mass include the presence of fat and certain calcification patterns on the mammogram and features of a simple cyst on the sonogram. Management decisions for other circumscribed masses will depend on characteristics such as shape, margins, calcification, multiplicity, size, stability, and sonographic features as well as patient age and risk factors. Most nonspecific circumscribed masses should be followed rather than biopsied as they are commonly present on mammograms and have a change of malignancy of less than 5%. Even when biopsied on the basis of interval change, most small circumscribed cancers will not have metastasized to the regional nodes. For palpable breast masses, selection of mammography or ultrasonography as the primary imaging modality will depend on patient's age and risk factors.