Sudden infant death syndrome (SIDS) has been present since antiquity. Indeed it is described in the Old Testament of the Bible: 1 Kings 3:19 ‘‘And this woman’s child died in the night.’’ “Cot death” was well known to pathologists, but not to paediatricians as they never saw them, as the deaths occurred in the home. These deaths were often labelled as pneumonitis (inflammation of the lung). It was not until 1965 that a specific International Classification of Diseases (ICD) code was allocated for SIDS. SIDS is the scientific term for a sudden unexplained infant death. These deaths generally occur during a sleep, and no cause is found despite a detailed examination of the death scene, medical history and thorough autopsy. Nowadays 50+% of deaths occur in a bed sharing context, so using the term “cot death” is inappropriate. The cause of deaths associated with bed sharing may be labelled as accidental asphyxia (i.e. suffocation), SIDS (that is unexplained) or unascertained (often used when the pathologist cannot distinguish between suffocation and SIDS). The trouble is that one pathologist or coroner might call the death SIDS and another accidental asphyxia. Sudden unexpected death in infancy (SUDI) captures all three causes, including unexplained and explained.