Objectives: Test the hypothesis of an underestimation of infant homicides in mortality statistics in France; identify its causes; examine data from the judicial system and their contribution in correcting this underestimation. Methods: A retrospective, cross-sectional study was carried out in 26 courts in three regions of France of cases of infant deaths submitted to the courts, 1996-2000, with follow-up of their files until case closing (1996-2008). For each case, cause of death established by the courts was compared with ICD cause of death as coded in official mortality statistics. Results: We examined 247 cases. Shortcomings in investigations were noted (autopsies: 75% of cases; fundus examination: 11%; diagnosis of sudden infant death syndrome [SIDS] without autopsy: 41%). Eighty deaths were considered homicides by the courts. Homicide rates in the court study are 2-3.6 times higher than those in mortality statistics. Nearly 1/3 of "accidental" deaths and 1/4 of deaths from unknown cause in mortality statistics are homicides. Mechanisms of underascertainment are: physicians' inappropriate death certification and underreporting of suspicious cases; inadequate investigation of cases; incomplete communication of final medical and forensic results to the mortality statistics department. Conclusions: In a country where neither transportation of the body to a hospital nor autopsy is obligatory, judicial data can make an important contribution to correcting mortality statistics. Practice implications: This study led to the first French protocol for investigating sudden unexpected deaths in infancy (SUDI). The protocol includes a physician "training" section focused on understanding the symptomatology and risk factors of violence, as well as the quality of death certification. (Contains 6 tables.)