The importance of diagnostic imaging in evaluating therapeutic response of bone sarcomas has increased with the use of chemotherapy administered before radiation therapy or surgery. The information provided by imaging studies is used to estimate prognosis; modify preoperative chemotherapy; and plan radiation therapy, surgery, and postoperative chemotherapy. This review examines the value and illustrates some pitfalls of traditional imaging methods, including conventional radiography, angiography, CT, and radionuclide scintigraphy, and discusses recent efforts to monitor therapy by using MR imaging and MR spectroscopy.