Cotard became particularly interested in cerebrovascular accidents (commonly known as 'strokes') and their consequences and undertook autopsies to better understand how these affected the brain. In 1869, Cotard left Salpêtrière, and at the outbreak of the Franco-Prussian War, he joined an infantry regiment as a regimental surgeon. Cotard moved to the town of Vanves in 1874, where he remained for the last 15 years of his life. He made particular contributions to the understanding of diabetes and delusions. In August 1889, Cotard's daughter contracted diphtheria and he reportedly refused to leave her bedside for 15 days until she recovered. He eventually contracted the illness himself and died on 19 August.