Simultaneous sudden infant death syndrome (SIDS) in twins is an extremely rare event. Some believe these are natural deaths, whereas others suggest they are unnatural. We report monozygotic twins dying at 12 weeks of age. Extensive investigation concluded that the cause of death was natural. Our case fulfilled the criteria of simultaneous SIDS in twins. However, thermal stress due to excessive thermal insulation, use of a pillow and placing twins in the same cot all represent a potentially unsafe sleeping environment. We recommend the term "simultaneous sudden unexpected death in infancy of twins" to describe such cases.