A visualization system for simulating nellrosurgical operations and helping in the orientation during neurosurgical procedures is presented. The system generates 3D and 2D reconstructions from preopertive M R and CT images. These reconstrllctions help in conjunction with intraoperative ultrasound the neurosurgeon in localizing the target in the brain tissue before craniotomy and during the opertion. The system is controlled by a mouse or speech in preoperative planning, while during the operation the neurosurgeon needs to use only voice control tlws leaving hands free. The flexible, expandable and portable design allows the visualization system to grow with the neurosurgical workstation.