An operation to remove half a child's brain sounds like something that only a mad--not to mention sadistic--scientist would dream up. And yet Dr. Benjamin Solomon Carson, a pediatric neurosurgeon at the Johns Hopkins Medical Center in Baltimore, Md., is neither insane nor cruel. His reason for performing the surgery--known as a hemispherectomy--is quite compelling. For young patients with rare seizure disorders, it is often their best chance of living a more nearly normal life.

Until Carson and his colleagues at Johns Hopkins came along, however, hemispherectomies had largely been abandoned because they so frequently resulted in death. He dramatically...