Back-related injuries have become a major health problem in the workplace, affecting as many as 35 percent of the work force and accounting for about 25 percent of all compensation claims. This study evaluates a back injury prevention program among employees in a northern California county in 1989-90. Six divisions of the county government were selected for the study because they had the highest prevalence of back pain experienced and the most back-related injuries in recent years. Four of the six divisions were randomly selected as the intervention group and the remaining two, the control group. Overall, 77 percent or 205 of the targeted employees in the intervention group participated in the study. The intervention group was given an identical health risk assessment (HRA) before and after the 1-year back injury prevention program that offered employees a combination of education, training, physical fitness activities, and ergonomic improvement. The control group was neither given the HRA nor offered the program. The back injury and cost data of both the control and intervention groups were collected before and after the 1-year intervention. The results showed a modest overall decline in back pain prevalence rates, but significant improvement in satisfaction and reduction in risky behaviors. Cost-benefit analysis showed the net benefit of introducing back injury prevention program was $161,108, and the return on investment is 179 percent. Therefore, the study offers suggestive evidence for the initial benefits of a back injury prevention program and lends support to the widely held belief that health promotion in the workplace can reduce employee health risks, increase healthful behaviors and attitudes, and improve attitudes toward the employer organization.Whether such intervention will continue to reap benefits in future years depends, to a large extent,on a favorable work environment and the maintenance and continuation of positive behavioral changes.