A persistent obstacle to accurate diagnosis and treatment of brain disease has been the difficulties in safely obtaining representative biopsy material in a live patient. Major problems are the variability in the anatomy between individuals and the inability to reliably locate deep structures through reliance on surface anatomic features. Although stereotaxic devices have been available for many years, they have now been supplanted by frameless systems, which are more accurate and less cumbersome and allow good surgical access and provision of intraoperative feedback of instrument location.