Numerous recent epidemiological studies have helped to better define the risk and protective factors for sudden infant death syndrome (SIDS). Method - Review and analysis of the most recent and relevant epidemiological studies selected through a search of the PubMed database. Results - Several epidemiological factors were identified. Some are well-known (sleeping position, smoking, vaccinations, opioids), but others stand out, such as sharing a bed or sofa as a risk factor, and sharing a room and the use of pacifiers as protective factors. Furthermore, it now appears that SIDS occurs more frequently when a family’s socioeconomic conditions are unfavorable, likely because prevention messages are harder to implement in such settings. Finally, moving away from the initial concept of SIDS, we now prefer to refer to unexpected deaths (UID), for which it is important to identify child abuse. Conclusion - The dramatic decline in the number of sudden infant deaths (SID) in France, and generally in Western countries, represents a major public health success, achieved thanks to the findings of epidemiological studies. (R.A.)