AlloDerm? (LifeCell Corp.; Brancburg, NJ) is an acellular dermal matrix (ADM) that serves as an immunologically inert scaffold in plastic surgery. In breast reconstruction, it is used as a filler for lumpectomy defects and can be used to create the inferolateral portion of the tissue expander pocket or implant pocket in postmastectomy patients. However, there are limited reports of the radiologic findings of AlloDerm? in patients who have undergone postmastectomy reconstruction. Familiarity with the imaging features of AlloDerm® is essential for correct diagnosis.We report the ultrasonography features of AlloDerm? in a 43-year-old female patient 3 months after postmastectomy reconstruction. It may help distinguish AlloDerm? from tumor recurrence or other foreign body materials such as gossypiboma. This is important as misdiagnosis can often lead to unnecessary surgical intervention.