The PÉLAGIE study was set up in response to concerns about the health of children and adolescents due to the presence of toxic compounds in our everyday environments in France. The study was set up in Brittany, France, in 2002. Over 3.5 years, it included 3,421 pregnant women during their first antenatal visit in three Breton departments (Ille-et-Vilaine, Côtes d'Armor, Finistère). These women and their babies were followed up at birth, then at 2 years (2004-2008), 6 years (2008-2012) and between 10 and 16 years (2015-2022) through a questionnaire sent to the parents and/or the child or adolescent. At each follow-up, questions were asked about the environment and health during childhood. A sub-group of children (1 in 10) was randomly selected from the cohort for more in-depth monitoring of cognitive and psychological development at around the age of 6 and of brain function using medical imaging at around the age of 10-12. Another sub-group of children (1 in 7) was chosen to monitor their pubertal development at around 12-13.