This article explores contestations over what constituted medical personnel, hospitals, and ambulances during the South African War (1899 – 1902). It shows that Boer fighters and British soldiers held differing conceptions of what constituted medical ‘neutrality’ and the meaning of the 1864 Geneva Convention. Analysing their contests over ‘neutrality’, it shows their diverse legal understandings were influenced by pre-existing medical cultures, the nature of guerrilla conflict, and British portrayals of the Boers as ‘uncivilised’ and so outside the realm of international law. These contests shaped the provision of medical relief on the ground in South Africa and generated international legal changes which echoed through later warfare.