All the MR exams of primary bone tumors performed during ten years were reviewed by three different radiologists. In all, 484 exams in 220 patients were considered--namely, 160 exams (33.1%) for staging purposes, 219 (45.2%) during therapy and 105 (21.7%) performed more than 8 months after the last treatment. Its well-known accuracy in the assessment of intra/extraosseous spread confirms the major role of MRI in the staging of primary bone tumors. During treatment, the overall accuracy of this method decreased to 88.8% because of the presence of therapy-induced tissue changes. MRI was 95.2% reliable in the detection of persistent disease or relapse in the exams performed long after therapy. Conventional radiology is still the method of choice in the study of primary bone tumors at presentation as it detects the lesion, differentiates malignant tumors and usually suggests the possible histotype. Nevertheless, MRI seems to be needed to depict actual tumor extent and to find the correct therapeutic approach. In the follow-up, MRI is the best single method to assess the response to therapy and to detect tumor persistence.