The classification of the cause of unexpected infant deaths by both pathologists and researchers may be quite inconsistent. For example, if an infant is found lying face down on soft bedding the death may still be certified as 'sudden infant death syndrome (SIDS)', 'accidental suffocation', 'undetermined', 'unclassified sudden infant death (USID)', or 'sudden unexpected death in infancy (SUDI)'. As the San Diego definition of SIDS does not appear to be rigorously or consistently applied, clarifying 'mechanical asphyxia not determined with certainty' may help to more clearly separate SIDS from USID. Including a classification algorithm with the definition may also help to better define unsafe sleep factors and suffocation. This commentary reviews the current situation with regard to classifying these deaths and concludes that the absence of diagnostic pathological markers with conflicting classification systems has led to idiosyncratic certification practices.