In France, there are significant social and geographic disparities in mortality rates around birth and during the first year of life. The department of Seine-Saint-Denis, which has had perinatal and infant mortality rates 30 to 50% higher than the French average since the late 1990s, is a striking example of this. Initiated by the Île-de-France Regional Health Agency to improve these indicators, the RéMI project (Reducing Infant and Perinatal Mortality) enabled the joint analysis of information from various public data sources to better understand the specific characteristics of the department related to these high mortality rates, prior to an audit of all perinatal deaths over a one-year period. This article presents a summary of these analyses, which focus on the characteristics of the pregnant population, their prenatal care, and pregnancy complications in cases of death, as well as the results of a Delphi consensus process involving professionals in the department to gather their opinions on the causes of this high mortality. Our results highlight issues with prenatal care (late initiation, few visits), particularly among foreign women, and stillbirths more often linked to very early deaths (22–26 weeks of amenorrhea) and hypertensive disorders. However, we did not identify any specific causes of neonatal deaths. The consensus process yielded hypotheses regarding the role, in these poor departmental indicators, of factors related to access to care and care coordination.