Karl Oskar Medin (August 14, 1847 – December 24, 1927) was a Swedish pediatrician. He was born at Axberg, Örebro and died in Stockholm. He is most famous for his study of poliomyelitis, an illness often known as the Heine-Medin disease, named after Medin and another physician, Jakob Heine. He had also influenced the study of meningitis and tuberculosis.
Medin received his doctorate in 1880 from the Uppsala University. He was appointed extraordinary professor at the Karolinska Institute in 1883 and went on to become professor of paediatrics the following year. He became professor emeritus in 1914.
In recognition of his polio research accomplishments he was elected posthumously to the Polio Hall of Fame in Warm Springs, Georgia, which was dedicated in January 1958.