On the evening of March 14, 1881, Emory Upton inexplicably & unexpectedly committed suicide. He was acknowledged as the U.S. Army’s leading tactician of his day; his drill manual had been officially adopted by the Army in 1867. For the past century, a mystery has remained as to the medical factors that led to his suicide. This paper examines the existing medical records & offers a probable modern diagnosis for this unique 109-year-old case report. (35 refs.)