 He then continued with further training in his chosen speciality of surgery, studying and working from 1922 in the Royal Infirmary of Edinburgh with Harold Stiles and David Wilkie.By 1925, Illingworth had qualified FRCSEd (Fellow of the Royal College of Surgeons of Edinburgh).In the period 1926–7, he studied abroad at the Barnes Hospital, St Louis, Missouri, USA (now the Barnes-Jewish Hospital)