Born at Toronto on 22 August 1882, son of Walter Balfour, who came from Scotland and was afterwards President of Balfour Tools, and his wife Alice Church, a Canadian by birth, he was educated at Hamilton (Ontario) Collegiate Institute and Hamilton General Hospital under Dr Ingersoll Olmsted. He was house surgeon at the Hamilton City Hospital, and in 1907 went to the United States as assistant in pathology at the Mayo Clinic, Rochester, Minnesota, where he remained for the rest of his life. He was appointed clinical assistant, Mayo Clinic 1908, junior surgeon 1909, and head of a section in the Division of Surgery 1912; Professor of Surgery, Mayo Foundation (University of Minnesota) 1923; Associate Director, Mayo Foundation 1935, and Director 1937. He retired in 1947 as Emeritus Professor and Emeritus Director. He equipped Balfour Hall at the Mayo Foundation House, endowed the Balfour Educational Fund, the Donald Church Balfour visiting professorship in the Mayo Foundation, and the Donald Church Balfour lectureship at the University of Toronto. Balfour was principally interested in the surgery of the stomach and duodenum; he published, with G B Eusterman, *The stomach and duodenum*, 1935. He was President of the American College of Surgeons 1935, and an Honorary Fellow of the Edinburgh, Australasian, and Canadian Colleges of Surgeons, and of the Royal Society of Medicine, the Association of Surgeons, the Académie de Médecine, Paris, and the American Gastroenterological Association. He was awarded honorary degrees by many universities. Donald Balfour married in 1910 Caroline, daughter of Dr Will Mayo, Hon FRCS; her sister married Dr Waltman Walters, senior surgeon to the Mayo Clinic; Dr Charles Mayo, Jnr, Hon FRCS, son of Dr Charles Mayo, Hon FRCS, was Mrs Balfour's first cousin; she died in 1960 leaving a daughter and three sons, two of whom are medical men. They lived at 200 First Street, South West, Rochester. Outside his profession Balfour was a keen musician, and a skilled performer on the organ and piano; he also studied the archaeology of the American Indians, particularly those of the South-West United States. He remained keenly interested in Canadian affairs and in Britain and her relations with both Canada and the USA. He died at Rochester on 25 July 1963, aged 80 years and 11 months.