Thanatobiochemistry refers to a post mortem study of biochemical parameters enabling to shed light on a cause of death. This discipline shines when suspected lethal pathology doesn't have any noticeable macroscopic or microscopic features such as diabetic ketoacidosis. We relate the case of fourty-five years old patient followed-up for type I diabetes mellitus, discovered dead at home, for which only post mortem biochemical exploration of vitreous humor allowed to determine the cause of death by diabetic ketoacidosis.