We report the use of CT-guided stereotaxic system to implant Ommaya reservoir in 26 patients with cystic brain tumors consisting of 16 gliomas, 3 craniopharyngiomas, 3 metastatic brain tumors and 5 other and unknown pathologies, on the way of their biopsy. The entire procedure was carried out in the CT room using Leksell's CT stereotaxic system. In 24 cases with supratentorial tumors, it was at the option of the operator to take any approach such as frontal, posterior temporal and parietal approaches. Especially in 3 cases of craniopharyngioma, we inserted the tube into their cyst directly so that the ventricle should not be open to the cyst. Also in cases of a pontine glioma and a C-P angle metastatic tumor, we used retromastoid approach to the posterior fossa by making patient's heads turned about 30 to 40 degrees to contralateral side of the approach, with slight flexion of the neck. Minimal bleeding occurred during operation in one case, however, it showed no clinical symptoms. Advantages of this method are as follows: Operative invasion is minimal; The surgeon can check the course of the cannula and position of the tip of Ommaya tube even at operation, and can modify it, if necessary.