Total and lifestyle-related medical care costs for employees of a major corporation participating in a worksite health promotion (WHP) program over a three-year period were compared with the costs for non-participants in a cross-sectional study. The study population consisted of 8,334 active employees based in the Cincinnati headquarters of The Procter & Gamble Company. Adjusting for age and gender, participants (n = 3,993) had significantly lower health care costs (29% lower total and 36% lower lifestyle-related costs) when compared with non-participants (n = 4,341) in the third year of the program. Similarly, in the third year of the program, participants had significantly lower inpatient costs, fewer hospital admissions, and fewer hospital days of care when compared with non-participants. No significant differences in costs were found between participants and non-participants during the first two years of the WHP program. Conclusions drawn from this study are that long-term participation in a WHP that includes high-risk screening and intensive one-on-one counseling results in lower total and lifestyle-related health care costs, as well as lower utilization of hospital services.