Employers need to control health costs while also keeping their workers healthy, productive and on the job. To those ends, BP America leased space to a full-service health and wellness center clinic on its Houston West-Lake campus, where rates of asthma, diabetes, coronary artery disease and other chronic conditions are high. Despite growing interest in worksite clinics, there is remarkably little quantifiable evidence demonstrating their value. This study uses a comprehensive value-chain approach to compare utilization, clinical outcomes and medical and pharmacy costs for medical center users and nonusers in Houston and other BP locations. Return on investment is also estimated. Overall utilization at the WestLake campus spiked in the 2012 plan year, pushing medical and pharmacy cost trends higher and highlighting the importance of shifting community-delivered services to the worksite medical center. Medical center users had fewer emergency room, inpatient hospital and outpatient hospital visits than nonusers as well as higher generic dispensing rates. While ROI fell slightly short of the break-even point in the medical center's first year based on an "intent to treat" methodology, indicators suggest that utilization and outcomes are moving in the desired direction.