Serial fluorine-18 bone scans and skeletal surveys were evaluated for usefulness in the staging of initial disease and for detection of metastases in children with osteosarcoma or Ewing's sarcoma. Scintigraphy was more sensitive than skeletal surveys in the detection of bony metastases in both tumors, but was less sensitive than radiographs for the detection of pulmonary lesions. Bone metastases did not occur before pulmonary metastases in patients with osteosarcoma but did in patients with Ewing's sarcoma. The effect of radiation therapy on the distribution of fluorine 18 throughout the bony skeleton is discussed.