Decisions regarding surgical treatment of cerebral tumours depend on the nature and the operability. A tumour which is easily accessible without functional risk can be operated on immediately even if there is some doubt as to its precise nature. In the case of an anatomically ill defined tumour in an area of high functional risk, surgery should not be considered before undertaking stereotaxic investigation. This allows confirmation of (in 8% of cases) correction of the diagnosis and provides the surgeon with precise anatomical information enabling him to choose the most effective and least traumatic means. Therapeutic results are analysed in function of histological grade and reduction or otherwise of the tumour by surgery of interstitial radiotherapy. The interest and limitations of stereotaxic investigation are discussed and therapeutic results analysed. We conclude that : 1) convincing histological evidence is required before deciding on radiotherapy and chemotherapy ; 2) age and functional state are important factors in prognosis ; 3) tumoral reduction by surgery renders radiotherapy and chemotherapy more effective.