A special-purpose robot system has been developed for neurosurgery. It contains control mechanisms developed from flight-simulator experience to allow precise motion and force-control using very low-force input. The robot constrains the tool motion to a safe region using methods developed for robotic surgery. These regions are defined pre-operatively using MRI segmentation techniques developed with the help of a simulator, ROBO-SIM. The intraoperative target location is tracked in real-time using ultrasound transducers. By applying updates using the ultrasound probe, safety is maintained by compensating for brain-shift. The overall system is being evaluated on phantoms.