In many clinics, intraoperative sonography is used as a routine method in neurosurgery. The availability of sterilizable applicators in diverse shapes and sizes enables the optimal approach to the site to be examined. Intraoperative sector scanning enables routine imaging of the entire anatomy of intracranial and spinal spaces. Almost all of the pathological processes can be exactly localized. Cavities filled with aqueous fluids like ventricles, arachnoidal cysts, cystic low-grade gliomas are shown as regions of low echo intensity. Other pathological processes are usually imaged by their hyperecho-characteristics: brain oedema has an increased reflexion compared to normal brain tissue; all brain tumors are diffusely echogenic, the image allows preliminary grading e.g. of gliomas. At the end of a removal of an intracerebral tumor lesion (e.g. glioma) it is possible to check if a radical resection was achieved. Vascular processes like aneurysms and angiomas are well defined by wall- and perfusion characteristics. Blood vessels might be identified with color-doppler studies. Ultrasound guiding enables even the most minutely detailed microsurgical approach; cysts and disorders of CSF circulation can be treated by simple ultrasound-monitored catheterization. Even stereotactic biopsy can often be replaced. Complications, such as hemorrhages, are recognized immediately.