Posterior echo attenuation on breast ultrasound is primarily associated with fibrosis or large calcifications. The description of the posterior echoes of a nodule by breast ultrasound is reflective of the acoustic attenuation characteristic of the mass compared to the surrounding tissue. Generally well-differentiated breast cancers result in nodules that show enhanced or significantly altered posterior echoes, whereas echo attenuation is more likely to result from benign breast disease. Posterior echo attenuation of the mass, also known as acoustic shadowing, is a dark area behind the mass that is usually associated with fibrosis as well as large calcifications, with or without cancer. Fibrous tumors, postoperative scarring, and breast cancer can cause echo attenuation behind the mass. Patients are advised to consult a specialist for an initial evaluation based on other descriptions in the ultrasound report and to follow up with follow-up examinations and treatment as prescribed.