Stereotaxic biopsy of cerebral tumors has been considerably facilitated by the use of CT scanner. A new method is described using the CT section in the horizontal or oblique plan of biopsy. When this has been determined, it is possible to define a trajectory, calculated by the CT scan computer, with external landmarks marked on the skin. This method is possible with any kind of CT apparatus; the surgical biopsy is performed in the operating room with a simple stereotaxic frame square-shaped and fixed in the plan of the CT section. The biopsy needle may be oriented in an antero-posterior or medio-lateral direction. This method has been used in 33 patients, leading to as precise histological diagnosis in 30 cases. No complications have been noted, except for transient neurological deterioration in two cases, due to local edema. Hemorrhage have not been observed. The topographical precision of the method was verified by the injection of lcc of air followed by a post-biopsy CT scan. This technique seems particularly valuable for the diagnosis of deep or wide spread hemispheric tumors, non indicated for open surgery.