Computerized tomography (CT) has become the natural imaging partner during stereotactic brain operations. At last a radiographic technique has been developed that actually visualizes the target and surrounding brain. Used intraoperatively, CT confirms accurate position of the probe, monitors biopsy or lesion techniques, immediately assesses results, and reduces the risks of operative complications. When appropriate markers are provided in the CT image, the CT computer rapidly generates target coordinates by converting CT coordinates to stereotactic frame coordinates. The same CT computer can be used to preselect the best trajectory and preplot the probe's path before insertion, using each patient's own "CT brain map." An accuracy of 1 mm has been achieved. The range and purpose of using an integrated CT-stereotactic system in the assessment of 11 patients with deep brain lesions is described. Operations are performed with the patient placed in the CT scanner. The stereotactic frame, constructed with low-atomic-number materials, permits nearly artifact-free CT images. With this stereotactic approach, CT has become part of the surgical armamentarium. Stereotactic surgery will soon be performed in an operating room equipped with such a "therapeutic" scanner.