Background: Although the prevalence of metabolic syndrome has been studied in nationally representative populations, little is known about its prevalence specifically among working adults. Because corporations are often the primary payers of health-care costs in the United States, they have a vested interest in knowing the impact of metabolic syndrome in employed individuals. Methods: A total of 4188 employees (83.4% male, 92.1% Caucasian, average age 40.8 years) of a midwestern U.S. manufacturing corporation participated in a health risk appraisal and biometric screening in 2006 and also used the company's medical plan. Those with metabolic syndrome were compared to those without metabolic syndrome in terms of their 2006 health risks, health conditions, health-care costs, pharmacy costs, short-term disability costs, and a measure of on-the-job productivity loss known as presenteeism. Results: A total of 30.2% of employees met the criteria for metabolic syndrome and were more likely to also have a variety of additional health risks and health conditions compared to those without metabolic syndrome. For example, 9.4% of those with metabolic syndrome self-reported having diabetes compared to 1.4% of those without metabolic syndrome. Health-care costs, pharmacy costs, and short-term disability costs were significantly higher for those with metabolic syndrome compared to those without metabolic syndrome, and increasing numbers of metabolic syndrome health risks were associated with greater numbers of employees reporting on-the-job productivity losses (presenteeism). Conclusions: Because metabolic syndrome is prevalent among the employees of this manufacturing company and is associated with significant economic costs, employers would be wise to address the health risks of employees through health promotion programs and benefit plan designs that help individuals improve their health and receive appropriate health screenings and medical care.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78143/1/met.2009.0008.pd