A 66-year-old male presented with a right breast mass, enlarging insidiously over a one-year period after trauma to the site. After the findings were attributed to glandular injury and hematoma, the patient eventually underwent mammographic and ultrasonographic evaluation that demonstrated masses in the breast and the axilla. A subsequent ultrasound-guided biopsy of the breast mass yielded a diagnosis of fibromatosis. However, the imaging features were suggestive of malignancy. Surgical resection was performed and revealed dedifferentiated liposarcoma-a neoplasm with components of well- and poorly differentiated liposarcoma as well as nonlipomatous sarcoma. This tumor type is primarily described in the retroperitoneum and limbs and is especially rare in the breast. We report an unusual case of multifocal primary dedifferentiated liposarcoma involving the breast in a man.