Understanding the Problem About 4,300 US infants die suddenly and unexpectedly each year. We often refer to these deaths as sudden unexpected infant deaths (SUID). Although the causes of death in many of these children can't be explained, most occur while the infant is sleeping in an unsafe sleeping environment. Researchers can't be sure how often these deaths happen because of accidental suffocation from soft bedding or overlay (another person rolling on top of or against the infant while sleeping). Often, no one sees these deaths, and there are no tests to tell sudden infant death syndrome (SIDS) apart from suffocation. To complicate matters, people who investigate SUIDs may report the cause of death in different ways and may not include enough information about the circumstances of the event from the death scene.