Yealland moved to London during World War I and worked at the National Hospital for the paralyzed and epileptic; there, he mainly dealt with cases of hysteria. Yealland did not considershell shock an illness, and he believed men showing such symptoms displayed a lack of discipline or sense of duty. He practised a form of therapy based on punishment. He was an exponent of auto-suggestion. He gained a reputation for curing and sending his patients back to the trenches quickly. Yealland published his wartime findings in Hysterical Disorders of Warfare in 1918. Allegedly, Yealland claimed a success rate of 100 per cent, and while his methods of treatment were regarded as particularly unethical by the academic discourse of the 1980s, more recent research suggests that his poor reputation might have come about owing to an over-representation of successful cases in Yealland's own works.