With the beginning of the war many students and teaching staff were drafted into military service, which led to a sharp fall in enrolment numbers in the first year of the war (from 235 enrolments in 1914 to 96 in 1915). In the winter semester of 1916/17, 90 prisoners of war, most of them from Germany, were admitted to study in St. Gallen.
In the winter of 1918/19, HSG was closed owing to the Spanish flu pandemic.