Possible health effects of exposure to low-intensity electric and magnetic fields (EMFs) are receiving increased attention in the scientific literature and, especially, in the public media. Laboratory research at the cellular and whole animal level has demonstrated various biological effects that may be related in some manner to the effects of EMF exposure on people. However, the exact mechanisms of this relationship are far from clear. The studies suggest that EMFs might be cancer promoters but are unlikely to be cancer initiators. At the level of human epidemiology, approximately 50 studies have examined the possible correlation of EMF exposures with adult and childhood cancers. Although the possibility of a correlation is weak, it cannot be discounted, and further research is needed. In the meantime, a practice of “prudent avoidance” of prolonged exposure to EMFs is warranted.