This study was undertaken to determine if a progressive correlation exists between body mass index (BMI), health care costs, and absenteeism and to identify an economically optimal BMI. We studied 3,066 First Chicago NBD employees by using health risk appraisals and personnel data. Analysis was completed for those employees with and without a risk for BMI. People at risk for BMI are more likely to have additional health risks, short-term disability and illness absence, and higher health care costs than those not at risk for BMI. A "J-shaped" curve between health care costs and BMI exists, with the low point occurring at about 25 to 27 kg/m2. We concluded that indirect and direct costs to an employer increase with increasing BMI. Employers may benefit from helping employees achieve a healthy weight. The initial target population should be those who are at highest risk of complications from obesity.