Calls for transparency in health care prices are increasing, in an effort to encourage and enable patients to make value-based decisions. Yet there is very little evidence of whether and how patients use health care price transparency tools. We evaluated the experiences, in the period 2011–12, of an insured population of nonelderly adults with Aetna’s Member Payment Estimator, a web-based tool that provides real-time, personalized, episode-level price estimates. Overall, use of the tool increased during the study period but remained low. Nonetheless, for some procedures the number of people searching for prices of services (called searchers) was high relative to the number of people who received the service (called patients). Among Aetna patients who had an imaging service, childbirth, or one of several outpatient procedures, searchers for price information were significantly more likely to be younger and healthier and to have incurred higher annual deductible spending than patients who did not search for price information. A campaign to deliver price information to consumers may be important to increase patients’ engagement with price transparency tools.