As a trainee of Dr. Harvey Cushing, cofounder and first president of the American Association of Neurological Surgeons, and founder of a prestigious international academic fellowship, Dr. William P. van Wagenen is an important figure in the history of neurological surgery. Perhaps less well known or appreciated is his seminal role as the first neurosurgeon to attempt, study, and publish results of the corpus callosotomy procedure for patients with epilepsy, and his collaboration with Andrew J. Akelaitis, which led to the description of some features of "split-brain" patients 2 decades before similar work in the 1960s eventually resulted in a Nobel Prize for Roger W. Sperry in 1981. These contributions firmly establish William P. van Wagenen as one of the founding pioneers in the surgical treatment of patients with epilepsy.