Childhood cancers result, like adult cancers, from multifactorial multistage processes, where environmental factors are likely to be involved. Thus, the role of ionizing radiation, well established at high doses, is discussed at low doses. Exposures to pesticides are discussed in several cancer sites. Exposures to road traffic and high voltage lines, delayed first contact with common infections, are suggested as risk factors of leukemia. However, the evidences remain insufficient to give rise to specific preventive measures, and the understanding of the role of the environment and its possible interactions with genetic factors are currently the subject of strong international research activity.