Intraaxial brain stem tumours are rarely treated by open surgical technique. In Bologna and Marseille, 23 and 10 stereotactic biopsies respectively were performed in patients with brain stem mass lesions. The mortality due to biopsy was 3% (1 pat.); while the morbidity was temporary in 6 cases (18%) and permanent in one patient (3%). The approach to the brain stem was via a frontal burr hole. 7 times, after biopsy and histological diagnosis, radioisotope implant of the neoplasm was performed with 125I (iodine). From the histological diagnoses of the lesions the following was found: only 40% of the young patients had highly malignant tumours; 83% of the adults had neoplasms (not all of the malignant type), while 17% of the verified lesions were non-neoplastic. Since a diagnosis of the lesion nature is impossible with current neuroradiological means, the authors noting a variety of masses found in their experience, emphasize the importance of stereotactic biopsy, as a scarcely invasive method to give a precise diagnosis and a possible treatment.