Experience with computed tomography (CT) in 25 patients with histologically proven osteosarcoma is presented. CT was as accurate as conventional radiographic methods in determining the presence of a lesion, but it was definitely superior in defining the extent of disease, particularly intramedullary extension and soft tissue extraosseous tumor component. CT was capable of demonstrating skip metastases in one patient. CT plays a key role in the preoperative evaluation of osteosarcoma patients, particularly when less than radical surgery is planned as primary treatment and when postoperative recurrence is suspected. CT is also useful in assessing the response to therapy in nonsurgical cases. The technique involved in the performance of this examination is discussed.