Excessive lead exposure can cause severe poisoning in children under 6 years of age. Indeed, young children are at higher risk due to their behavior (putting hands and objects in their mouths), because lead absorption through the digestive tract is much higher in children than in adults, and because they are more sensitive to its neurotoxic effects. The initial signs of poisoning are nonspecific, so screening for childhood lead poisoning relies on measuring blood lead levels. Lead is a cumulative toxin; with steady exposure, blood lead levels allow for the assessment of the internal lead dose. Excessive exposure is considered to be present when blood lead levels exceed 100 μg/L. However, health effects—particularly on a child’s intellectual development—cannot be ruled out even at lower levels. To accurately assess the level of lead exposure in screened children, it is helpful to have information on the degree of exposure among children living in the same area. The study reported in this article aims to assess the average blood lead levels of children residing in the vicinity of the town of Argenteuil, located in the urban area of Île-de-France. (R.A.)