The authors report the incidence of cancer in a large cohort of employees identified from all 99 Danish utility companies. Personal data and information on employment and exposure to magnetic fields and asbestos were obtained from manual files at the companies, the Danish Supplementary Pension Fund, and the public payroll administration. A total of 32,006 individuals with more than 3 months of employment were linked with the files of the Danish Cancer Registry. The period of follow-up for cancer occurrence among the employees was from April 1968 through December 1993 in the study conducted from 1994 to 1997. Overall, 3,008 cancers were observed, with 2,825 expected, yielding a small but significantly increased risk of 1.06 (95% confidence interval 1.03-1.10) among the utility workers in comparison with the general population. No excess was observed for all leukemias or for cancers of the brain or breast among men or women. There was no association of electromagnetic field exposure with risk of these cancers, even when the level and length of exposure to magnetic fields were taken into account. Increased risks for cancers of the lung and pleural cavity were seen mainly for workers whose jobs involved exposure to asbestos. The results from this study do not support the hypothesis of an association between occupational exposures to magnetic fields in the electric utility industry and the risk for cancer.