Computerized tomography has transformed the protocol of exploration and surveillance of diencephalic tumours. It gives information concerning their structure, extension and all associated pathology. In addition, the examination is non-traumatic for the patient which in most cases makes it possible to avoid classical neuroradiological procedures with contrast medium, and may be repeated in order to observe the course of these tumours after radiotherapy. Four cases are reported to illustrate the different contributions of CT scanning.