The community of neurosurgeons is relatively small. In the United States there are about 3,500 practicing board-certified neurosurgeons and only 99 approved training programs. Each year there are approximately 170 new training positions open and 160 residents who graduate. The total number of residents in the United States is about 790. Sub specialization has become a part of neurosurgery, and there are now post-residency graduate training positions or fellowships in pediatric neurosurgery, spine surgery, interventional neuroradiology, vascular surgery, neuro-oncology, pain, trauma, and functional and stereotactic neurosurgery.