Osteosarcoma arising in soft tissues is exceedingly rare in children. The tumor most often affects older adults, involves the lower extremity, responds poorly to chemotherapy, and carries a grave prognosis. The authors describe a 12-year-old girl with an extraosseous osteosarcoma of the left sternocleidomastoid muscle with pulmonary metastases. The patient responded well to neoadjuvant chemotherapy and remains disease-free nearly 3 years after her initial diagnosis. The authors review available information about this disease in children and adults. Children with extraosseous osteosarcoma may have a more favorable response to treatment than adults; thus, a curative approach using combined modality therapy appears warranted.