Sir Thomas Grainger Stewart FRSE FRCPE (23 September 1837, in Edinburgh – 3 February 1900, in Edinburgh) was an eminent Scottish physician who served as president of the Royal College of Physicians of Edinburgh (1889–1891), president of the Medico-Chirurgical Society of Edinburgh, president of the medicine section of the British Medical Association, and Physician-in-Ordinary to the Queen for Scotland. He was perhaps best known for describing the condition known as as well as directing scientific attention in Great Britain to the deep reflexes.