John Alfred Ryle (1889–1950) was a British physician and epidemiologist.
He was born the son of Brighton doctor R J Ryle and brother of the Oxford philosopher Gilbert Ryle. He was educated at Brighton College and Guys Hospital where he qualified in 1913. He served in the military during WWI and afterwards qualified MD at the University of London. After teaching at Guys Hospital he was appointed in 1935 Regius Professor of Physic at the University of Cambridge. In 1943 he was appointed chair of the newly created Institute of Social Medicine at the University of Oxford, initiating the academic discipline of Social Medicine (Epidemiology).
He was elected a Fellow of the Royal College of Physicians in 1924 and delivered their Goulstonian Lecture in 1925 and their Croonian Lecture in 1939.
From 1932 to 1936 he was Physician to King George V's household and then Physician Extraordinary to the king.
Ryle was politically active at Cambridge, helping Jewish scholars emigrate from Germany and Austria before World War II. During World War II, he was working at Guy's Hospital to help them prepare for the Blitz.
He had married Miriam P Scully in London in 1914. They had several children, including astronomer Martin Ryle.