The roof of the third ventricle is lying on the thalamus parts. When a tumor fills and expands the third ventricle it is always possible to lift up this velotrigonal roof like the cover of a box and to access to these lesions. The authors have approached 15 tumors of the third ventricle or pineal area by this route interthalamotrigonal about 78 cases of tumors operated in the Lille's neurosurgery department during 30 years. The technical possibilities are compared and the advantages of this route emphasized with usual access. The interthalamotrigonal access gives a great convenience during operation. It make easy the complete removal of removable tumors of the pineal area and the third ventricle. It is possible with minimum during operation and after effects for the patient.