Designing a US$94-million programme that draws big data from dozens of computer systems is an enormous challenge-just ask former Health and Human Services secretary Kathleen Sebelius who resigned last week after months of technical problems with HealthCarg.gov. But the ethical issues may prove an even higher hurdle. The United States would do well to watch the United Kingdom as it grapples with creating its own national database,care,data (see Narure 507, 7; 2014). Although the UK national health system is much more mature and cohesive than anything the United States has, the project's rollout has been delayed for months because of unanswered questions about informed consent and access to sensitive patient data.