The neuropathologist plays a crucial role in the care of patients with cancer of the brain. Neuropathologists examine the tumor tissue removed by the neurosurgeon in the operating room. Immediate examination of tissue that is frozen in the operating room using liquid nitrogen provides the surgeon with indispensable information. Often a preliminary diagnosis can be made which may determine if the operation can be stopped or if removal of more tissue is necessary. The final diagnosis requires careful examination of numerous tissue layers stained with different techniques and is usually not available until several days after surgery.