The French National Registry of Childhood Leukemias and Lymphomas (RNLE) was established in 1995 by Inserm Unit 170 in collaboration with French pediatric hematology-oncology treatment networks. The registry covers the population of children under 15 living in metropolitan France. Through retrospective data collection, the RNLE includes all cases of leukemia, myelodysplastic syndromes, and non-Hodgkin lymphoma (NHL) occurring since January 1, 1990, and all cases of Hodgkin’s disease (HD) since January 1, 1999. The RNLE has thus been monitoring the incidence of childhood hematologic malignancies for 15 years. It is also a powerful research tool for studying their risk factors. The registry conducts several ecological and case-control studies on the role of environmental and genetic factors in childhood hematologic malignancies. The authors describe here the cases of leukemia and NHL recorded in France during the period 1990–1999. This is the first report on the incidence of leukemia and NHL assessed on a national scale. (R.A.)