Although consumer-driven health plans (CDHPs) have grown dramatically, the question of whether CDHPs have reduced health care costs has not been answered definitively. This article presents what the authors believe to be the first study to analyze a large sample of claims data and to look in detail at different types of utilization among enrollees in a CDHP and those in a traditional comprehensive major medical (CMM) plan. After adjusting for the finding that CDHP enrollees are both younger and healthier than those in CMM plans, the authors found that CDHP enrollees show no consistent or significant utilization differences for measures over which consumers have little control (e.g., inpatient stays); lower utilization for measures over which consumers have greater control (e.g., emergency room visits); and higher utilization of preventive services.