The studies undertaken by Ontario Hydro to assess any possible risk of cancer from electromagnetic fields have added to the knowledge of the generation of 60 Hz electromagnetic fields in the human environment, and to their effects on cells, on small animals in the laboratory, on populations of workers in electrical industries, and on children. In general the results of these investigations support the comments and conclusions of the Working Group that was commissioned by the National Institute of Environmental Health Sciences in the U.S.(1998) to review this field. That is, they add to the plausibility and support the conclusion that electromagnetic fields are possibly carcinogenic to humans, although any risk is small. In addition, the research provides some rationale for the exposure guidelines such as those adopted by the International Committee for Non-Ionizing Radiation Protection. The Royal Society Panel monitoring the Electromagnetic Fields Risk Assessment Program of Ontario Hydro supports the conclusions of the NIEHS and suggests that it would be prudent to avoid long exposure to high fields as defined in the exposure guidelines of the International Committee for Non Ionizing Radiation Protection.