Purpose: To evaluate the clinical and sonographic (US) features of metastatic tumors from extramammary malignancies to the breast. Methods: This study included 23 patients with pathologically proven metastases in the breast. Two radiologists retrospectively analyzed the images from US (n = 23), mammography (n = 11), and MRI (n = 5) examinations according to BIRADS. Results: Patients presented with a palpable mass or diffuse breast swelling (21/23) or were asymptomatic (2/23). Eighteen patients had solitary or multiple breast masses on US. The common US finding was an ovoid hypoechoic mass with a noncircumscribed margin. The final assessment categories were BIRADS 3 (probably benign finding) in 6 cases (25%) and BIRADS 4 (suspicious abnormality) in 18 cases (75%). In five patients, US displayed a diffuse infiltrative pattern without a focal lesion, which was categorized as BIRADS 4. Conclusions: Metastatic tumors in the breast have a wide range of sonographic appearances, with some resembling benign lesions. Any newly developed mass in a patient with a known history of extramammary malignancy, even with a probably benign US appearance, should undergo biopsy for pathologic confirmation.