In 4 patients with aneurysmal bone csyts, radiologic findings of their conventional x-rays, 99mTc-MDP bone scans and CT scans were reviewed. On CT scans, 3 patients revealed so called "the fluid-fluid levels." It must be one of the specific findings which is able to diagnose the ABC. When we performed the ultrasongraphy in a patient with the balooig out lesion on right ilium. multiple horizontal echogenic lines were observed in the supine and decubitus position. It could be interpretated as a identicla finding to the fluid-fluid levels on CT. Therefore ultrasonography is also one of the specific diagnostic tools to detect the ABC. Transcatheter embolizaton was beneficial in reducing operation time and blood loss, and in supplying clear operation field.ion field.