Measuring patient safety is critical to improvement. This ethnographic study examined the implementation of a patient safety measurement program in the United Kingdom, the NHS Safety Thermometer, which measured incidence of pressure ulcers, harm from falls, catheter-associated urinary tract infection, and venous thromboembolism, with the goal of informing local improvement efforts. Investigators sought to examine how the measurement program was perceived by frontline staff. Despite the explicit emphasis on using the data for improvement, it was viewed as an external reporting requirement. The program was also viewed as a basis to compare organizations, especially because it included pay-for-performance incentives. The authors suggest that the intention of the program did not match the real-world considerations of participating health care systems and had the unintended consequence of creating potential for blame.