Background: Although most breast masses in children are benign, breast cancer must be considered in the differential diagnosis. The majority are represented by sarcomas and secondary lesions. Literature reports only four cases of neuroblastoma breast metastasis, with no emphasis on radiologic features. Our work aims to furnish a description of radiologic and sonographic features of neuroblastoma metastasis in the breast. Case description: A 15-year-old girl had a round nodular mass in the outer upper quadrant of the left breast that had rapidly enlarged over the last month. An ultrasound showed two subcutaneous nodules (3.8 cm and 1.3 cm in maximum diameter), with an irregular shape, heterogeneous echogenicity (isohypoechoic), and hyperechoic foci with a posterior acoustic shadow inside. Overall, the features were highly suspicious of secondary malignant lesions. Computed tomographic scan was performed and found a large retroperitoneal mass and multiple mixed secondary lesions to the spine and hip. A 14G core needle biopsy of breast masses was performed and showed a secondary localization of neuroblastoma. Conclusions: In adolescents, metastases are the most frequent cause of malignant breast masses. Ultrasound examination should be preferred as the first imaging tool. For the differential diagnosis of breast metastasis with benign masses, a rapid enlargement, a heterogeneous echogenicity, and intralesional hyperechogenic foci could be considered features of malignancy.