Fat necrosis is a common benign condition. It is associated with iatrogenic, penetrating or blunt trauma. In a number of cases, there is no history of injury. Mammographic presentation is either a typical lipid cyst or a spiculated lesion, mimicking malignancy. Ultrasonographic appearance is that of either a cyst, or solid mass, or an area of increased echogenicity. Calcifications may be present and are usually coarse or ring-like.