Acting on the suggestion of her top data crunchers at the department's Centers for Medicare and Medicaid Services (CMS), Health and Human Services Secretary Kathleen Sebelius released an enormous data file on May 8 that reveals the list-or chargemaster"-prices of all hospitals across the country for the 100 most common inpatient treatment services in 2011. It then compares those prices with what Medicare actually paid hospitals for the same treatments-which was typically a fraction of the chargemaster prices. As a result, Americans are a big step closer to being able to compare what hospitals charge them for goods and services with what they actually cost. There are two reasons Sebelius' release of this newly crunched, massive data file is a great first step toward a new transparency in health care costs. First, it reveals the vast disparity between what hospitals charge for pills, procedures and operations and the real cost of those services, as calculated by Medicare. The second reason the compilation and release of this data is a big deal is that it demonstrates [that] most hospitals' chargemaster prices are wildly inconsistent and seem to have no rationale. Thus the release of this fire hose of data-which prints out at 17,511 pages-should become a tip sheet for reporters in every American city and town, who can now ask hospitals to explain their pricing. In the through-the-looking-glass world of health care economics, those who are asked to pay chargemaster rates are often under-insured or lack insurance altogether. Moreover, insurers typically negotiate discounts off the grossly inflated chargemaster prices ($77 for a box of gauze pads!), so the chargemaster matters for insured patients too.