American medicine has long sought to control the standard of care that physicians are expected to provide to their patients. One effort to insulate the standard of care from external interference, called a “safe harbors” approach, would enable physicians to avoid liability for malpractice if they adhered to medical practice guidelines. The idea is to eliminate the “battle of experts” and reduce defensive medicine by requiring judges and juries to accept guidelines as conclusive evidence of the standard of care. Yet current efforts to improve the guideline development process, including the use of evidence-based guidelines, are unlikely to be able to overcome the shortcomings that led a similar safe harbors initiative to fail in the early 1990s. Moreover, there is no adequate justification for conferring this degree of self-regulatory power on the medical profession.