This category refers to deaths, in infancy and later in life, which are sudden, unexpected and for which no clinical cause has been identified.

Geographically, the map indicates that sudden death, cause unknown is more likely in Inner London, some urban areas of the north west and much of western Scotland. As the age–sex bar chart shows, most of these deaths occur in the first year of life.

This category includes sudden infant death syndrome or SIDS, also known as cot death in the UK and crib death in the US. Seventy-one per cent of the deaths in this category are of the under-ones.

SIDS is any sudden and unexplained death of an apparently healthy infant aged one month to one year. SIDS is a diagnosis of exclusion – that means it should only be used as the defining condition of death when all other possibilities have been excluded by means of a post-mortem, an investigation of the scene and circumstances of death, and an exploration of the medical history of the infant and their family.