This chapter provides an overview on health risks observed in populations (1) residing near nuclear test sites at the time of surface and atmospheric atomic bomb testing and (2) residing near nuclear facilities. While the external whole body dose received from nuclear bomb testing is estimated to exceed 1 Gy from certain tests, doses to the public from nuclear installations under normal operating conditions are estimated not to exceed a few μSv, which is less than 1% of the natural background radiation dose. For participants of nuclear bomb testing, an increased leukemia risk was reported from different studies, while the reporting on solid cancer gives inconclusive results. Among the general population an increased risk for thyroid diseases (cancer, nodules or autoimmune thyroiditis) was described in different studies. These findings are related to the exposure to iodine 131. For solid cancer there is an elevated risk reported from Kazakhstan amongst those having been exposed, but the hitherto uncertain dosimetry hampers the establishment of a dose–response relationship. The risk of leukemia seems to be elevated in a specific population group near the Nevada Test Site. The discussion of adverse health effects close to nuclear sites, in particular near nuclear power plants, is focused on the leukemia risk amongst children. Some studies showed systematically elevated risks in the closest vicinity of the sites and in the youngest age group (those below 5 years of age at time of diagnosis). The doses from the discharges are by far too small to explain the findings. Further research into the pathogenesis of childhood leukemia could help to understand the findings. Currently, the cause of the reported elevated risks of leukemia amongst children remains unclear.