PURPOSE: To evaluate the MR imaging findings of chondroblastic osteosarcoma. MATERIALS AND METHODS: Weincluded 11patients (8 men, 3 women, mean age of 19 years) with pathologically proven chondroblastic osteosarcomaand, as a control group, 20 patients with conventional osteosarcoma. We obtained pre- and post-enhanced MR imagesof all patients and retrospectively reviewed the signal intensity and enhancement pattern of tumors. MR imageswere correlated with histopathology. RESULT: In chondroblastic osteosarcomas, the major portion (< 75%) of thetumor showed low signal intensity on T1-weighted images and homogeneous high signal intensity on T2-weightedimages, but did not show enhancement. The margin of the area showed a lobular pattern. Enhanced nodules (n=11) andstrands (n=8) were seen in the nonenhanced portion. Histopathologically, the nonenhanced portion, nodules, andstrands revealed a chondroid matrix, hypercellular area, and fibrovascular septa, respectively. Conventionalosteosarcomas showed heterogeneous enhancement ; six showed a focal (<25%) nonenhanced area representing necrosis. CONCLUSION: Chondroblastic osteosarcoma showed characteristic MR imaging findings.