An adult, female white-tailed deer (Odocoileus virginianus) died due to acute arsenic intoxication in an intensively managed northern hardwood forest in northern New York. We hypothesize that the deer licked trees injected with Silvisar 550, which contains mono-sodium methanearsonate. We believe this is the first report of death of a free-ranging white-tailed deer, due to ingestion of monosodium methanearsonate.