William Leo Nyhan (born March 13, 1926) is an American physician best known as the co-discoverer of Lesch–Nyhan syndrome. Nyhan currently serves as professor of pediatrics at UC San Diego School of Medicine in La Jolla, California. He has held positions at Johns Hopkins School of Medicine and the University of Miami Leonard M. Miller School of Medicine and has served on a number of advisory committees, pediatric advisory boards, and research foundation boards.