We present an updated summary on risk factors for childhood malignancies, following to previous reviews published on Epidemiologia&Prevenzione and largely based on the monographs of the International Agency for Research on Cancer (IARC). Ionizing radiations are certain carcinogens, with evidence in humans, from studies both on children and on adults. Evidence specifically regarding childhood cancers is available also for other carcinogens, such as tobacco smoking, some solvents, some occupational activities of parents, and some viruses (HIV and EBV). For most carcinogens, information specifically regarding childhood cancer risks is limited, but it is enough to suggest the reduction of exposure, according to a precautionary approach. Available evidence can be helpful in evaluating reports of possible clusters of disease and the association with putative causes.