Laboratory and in vivo studies in primates, and serological evidence in humans, indicate that food animal oncogenic viruses show potential for causing cancer in humans. However, until fairly recently, supporting analytic epidemiologic studies have been lacking and have concentrated on lung cancer. We conducted an extensive Medline search and reviewed 60 studies investigating lung cancer risk in highly exposed workers in the meat and poultry industries. The overwhelming majority of studies of different designs (including all the cohort mortality and cancer incidence studies) indicate at least a 30% excess risk of lung cancer in meat and poultry plant workers, even after controlling for smoking. Evidence points to food animal oncogenic microorganisms as one of the main causes. This has important public health implications because the general population is also widely exposed. Studies carried out thus far have not had sufficient statistical power to investigate other potentially carcinogenic exposures within the industries. Thus, large studies that can adequately control for occupational and non-occupational confounding factors are needed, so that the possible role of food animal oncogenic viruses in the occurrence of human lung cancer can be clearly defined.