BACKGROUND: It is essential for children suffering from or at risk of lead poisoning to have regular follow-up, and specifically for their blood lead (Pb) levels to be monitored. The present study assessed the occurrence of late follow-up testing of blood lead levels in children in Greater Paris, and factors related to such delays. METHODS: Since 1992, the SSSIILF has been systematically recording data on lead levels in blood tests conducted for screening and follow-up in Greater Paris. For Pb greater or equal to 45mug/dL (Group 4), a further blood lead test has to be done within three weeks. For levels of 25mug/dL</=Pb<45mug/dL (Group 3) and 10mug/dL</=Pb<25mug/dL (Group 2), a second test must be done within 6months. For Pb less than 10mug/dL combined with one or more risk factors (Group 1: children at risk of poisoning), a second test is required within 6 to 12months. Children aged 1 to 6years who were screened between 1992 and 2002 were selected. The occurrence of late follow-up testing was estimated, and the independent effect of each variable associated with a delay was measured using a logistic regression model. RESULTS: Delays in re-testing were reported for 66.9% of Group 4 children (n=356), 45.3% of Group 3 children (n=921), 74.1% of Group 2 children (n=5 466), and 88.7% of Group 1 children (n=15 612). In the three groups with Pb greater or equal to 10mug/dL, there was better follow-up (i.e. less delay to re-testing) for children screened most recently, those whose initial blood lead test results were elevated, those who lived in sub-standard housing built before 1949, and those who lived in suburban districts of Paris. The delay was longer for children aged 4 to 6 compared to younger children. When the size of the group was large enough, these differences were significant. In Group 1, similar results were observed except for a home address in a suburban district. Furthermore, follow-up was better for children of Sub-Saharan African parents, children whose initial prescription had been issued by a "PMI" mother/child healthcare centre and children from large families. CONCLUSION: Despite substantial delays in carrying out follow-up blood lead level testing, these delays were shorter for the populations with the greatest exposure.