Medical savings accounts (MSAs) belong to a larger class of incentive-based health care plans. Using a model that allows the consumer to invest in healthy activities, we examine the efficiency properties of incentive plans and compare them to traditional full- coverage and deductible plans, under both experience rating and community rating. The model also is extended to include utilization of preventive health care. Properly constructed incentive plans have the capacity to induce socially efficient levels of healthy activities and preventive care, raising the expected wealth of consumers without reducing insurers' profits.