Background. Given the serious health consequences of lead poisoning (blood lead levels [Pb] of 100 mg/L or higher), the objectives of this study were to estimate the time required and to identify the factors associated with a return to blood lead levels below 100 mg/L, according to the severity of the poisoning. Methods. The surveillance system for childhood lead poisoning in the Île-de-France region (SSSIILF) has systematically recorded blood lead levels at initial screening and follow-up for children in the region since 1992. For children under seven years of age at the time of poisoning screening, the follow-up duration curves without a return to the 100 mg/L threshold and the relative risks (RR) of returning to a Pb level below 100 mg/L were estimated (Kaplan-Meier curves and Cox model), after categorization according to the level of poisoning (Group 4: Pb ≥ 450 mg/L; Group 3: 250 mg/L ≤ Pb < 450 mg/L; Group 2: 100 mg/L ≤ Pb < 250 mg/L; Group 1: Pb < 100 mg/L and presence of risk factors for poisoning).(R.A.)