Fourty-five patients affected by brain stem expanding lesions underwent serial stereotactic biopsy between 1978 and 1986. The definitive histological diagnosis allowed the definitive treatment of extrinsic tumours and non-neoplastic lesions. In patients affected from glial tumours the serial stereotactic biopsy allowed the histological grading and the definition of the growth modalities at the superior boundaries of the tumours. These data have been utilized to guide the choice of treatment. The future perspectives of stereotactic biopsies are discussed in view of the therapeutic results obtained in this series and in other series reported in the literature.