Rethinking the allocation of medical malpractice risks between patients and providers.

A distinctive feature of medical malpractice law is its acceptance of medical custom as the dispositive legal standard of care. Outside the field of medical malpractice, long established legal doctrine accords limited weight to custom in defining the general standard of care in negligence cases.' In medical practice, by contrast, the legal standard of due care is virtually defined by the customary skills and practices of the profession. A showing of subconformity to custom here ordinarily yields liability, while conformity ordinarily forecloses it; as a corollary, the metes and bounds of custom are required to be established by medical experts qualified to speak to the particular skills or practice in question.2 As there are always exceptions to the general rule, so also there are exceptions to the general exception: liability may be established without expert testimony or independently of professional custom in cases where negligence is obvious to the lay observer or where medical judgment is not implicated. 3 The justification for treating malpractice cases differently from other accident cases is by no means obvious or simple. Posner has suggested that a distinction might rest on the notion that custom in malpractice cases was used essentially as evidence of the parties' contractual expectations. 4 There is