Background. Sudden infant death syndrome (SIDS) may have several etiol
ogies, all of which must be identified in order to recognize those inf
ants believed to be at risk. One of the best ways to do this is by pro
spective studies on a large population of infants who died of SIDS. Me
thods. A total of 171 infants who died from SIDS between January 1, 19
86 and June 30, 1991, were studied. 154 infants were completely invest
igated, including a post mortem examination. They were assigned to one
of 4 groups, according to whether death was due to diseases of poor p
rognosis (group A), diseases that are occasionally fatal but potential
ly treatable (group B), minor diseases not normally fatal (group C), o
r was essentially unexplained (group D). Results. The classical risk f
actors for SIDS were found in this population: incidence peaked in mal
es (sex-ratio 1.5), during the cold seasons (62%), between 1 and 6 mon
ths of age (94%), mainly between 1 and 4 months of age (84%). Symptoms
were definitely present during the 2 days before death in 50%. 20% of
cases had clinical histories of congenital disease, complicated or re
current postnatal disease, or fulminant recent disease. Group A includ
ed 107 infants (69% of the 154 completely investigated patients). Prem
ature birth (17.5%) and low birth weight for gestational age (10.5%) w
ere more frequent in our series than in the normal population. Conclus
ion. The cause of death was identified in about 75% of cases. This pos
sibility improves management of further siblings of SIDS victims even
though the variety of risk factors makes prevention of SIDS difficult.