Recently, operative results of intramedullary spinal cord tumors have been greatly improved since the introduction of microsurgery. It is very important to know the precise size and location of the tumor prior to the operation so that we can approach the tumor with a minimum of damage to the spinal cord. However, it is not always possible to demonstrate the precise localization of the tumor preoperatively. In this report, we emphasize that intraoperative spinal sonography is very useful in determining the extent of the tumor and differentiating solid component from cystic component of the tumor. Methods and Materials We performed intraoperative spinal sonography on ten patients with intramedullary spinal cord tumor. This series included three cases of hemangioblastoma, three cases of astrocytoma, two cases of ependymoma, one case of subependymoma, and one case of mixed glioma. Eight out of ten cases were associated with cysts. The intraoperative spinal sonographic examinations were performed after laminectomy. The linear scanning probe of 5 or 7.5 MHz transducer was used. Results 1) Solid components The acoustic pattern of the solid tumor was either hyperechoic or iso-echoic. Six cases (three hemangioblastomas, two ependymomas, and one astrocytoma) were hyperechoic. Other four cases (two astrocytomas, one subependymoma, and one mixed glioma) were iso-echoic. 2) Cystic components The cysts associated with the tumor were anechoic in six out of eight cases, which were confirmed at surgery, and multiple cysts were identified.(ABSTRACT TRUNCATED AT 250 WORDS)