Cardiac rehabilitation and exercise training (CRET) provides health risk intervention in cardiac patients over a relatively short time frame. Worksite health programs offer a unique opportunity for health intervention, but these programs remain underused due to concerns over recouping the costs. We evaluated the clinical efficacy and cost-effectiveness of a 6-month worksite health intervention using staff from CRET. Employees (n = 308) and spouses (n = 31) of a single employer were randomized to active intervention (n = 185) consisting of worksite health education, nutritional counseling, smoking cessation counseling, physical activity promotion, selected physician referral, and other health counseling versus usual care (n = 154). Health risk status was assessed at baseline and after the 6-month intervention program, and total medical claim costs were obtained in all participants during the year before and the year after intervention. Significant improvements were demonstrated in quality-of-life scores (+10%, p = 0.001), behavioral symptoms (depression -33%, anxiety -32%, somatization -33%, and hostility -47%, all p values <0.001), body fat (-9%, p = 0.001), high-density lipoprotein cholesterol (+13%, p = 0.0001), diastolic blood pressure (-2%, p = 0.01), health habits (-60%, p = 0.0001), and total health risk (-25%, p = 0.0001). Of employees categorized as high risk at baseline, 57% were converted to low-risk status. Average employee annual claim costs decreased 48% (p = 0.002) for the 12 months after the intervention, whereas control employees' costs remained unchanged (-16%, p = NS), thus creating a sixfold return on investment. In conclusion, worksite health intervention using CRET staff decreased total health risk and markedly decreased medical claim costs within 12 months.