The implantable cardioverter defibrillator (ICD) is a costly new treatment for patients at high risk of sudden cardiac death. Randomized trials of the ICD showed it to be effective in some groups of patients but not in others. While new trials testing the ICD were ongoing to clarify the evidence, policymakers faced immediate decisions about providing insurance coverage for the device. The high cost of ICDs, the large population of patients potentially eligible to receive them, the potential to reduce preventable deaths, and the unsettled state of the medical evidence provided a challenge to evidence-based medicine and to policymakers.