Sir Harry Guy Dain FRCS (5 November 1870 – 26 February 1966) was a British physician.^[1]

Between 1887 and 1894 Dain studied science and medicine at Mason College (a predecessor college of the University of Birmingham). He graduated with a University of London external MB degree in medicine in 1894.^[1][2]

Dain was Chairman of the British Medical Association from 1943 to 1949 at the time of the creation of the National Health Service.^[1] He strongly opposed the creation of the National Health Service and led British Medical Association opposition to it, publicly clashing with Aneurin Bevan, the then Minister of Health.^[3]

Dain was knighted in 1961. Dain was elected a Fellow of the Royal College of Surgeons in 1945. He received an honorary LLD degree from Aberdeen University in 1939 and an honorary MD degree from Birmingham University in 1944.^[1]