This article is from the Sudden Infant Death Syndrome FAQ, by David Stokes firstname.lastname@example.org and Margaret D. Gibbs gibbsm@no_spam.poppyware.com with numerous contributions by others.
SIDS is the death of an apparently healthy infant that remains
unexplained after a thorough autopsy and death scene
investigation. There appears to be no suffering in most cases;
death occurs very rapidly, usually during sleep. SIDS is the
leading killer of infants between one week and one year with an
approximate rate of two per thousand live births (1 in 500).
6000-7000 babies die of SIDS every year in the US. The peak age
is around two to four months and the majority of the deaths occur
during the winter months (October to April in the Northern
Hemisphere). Researchers believe that SIDS probably has more than
one cause, although the final process appears to be similar in most
cases. SIDS can not predicted, prevented, or reversed.