Practice guidelines are proliferating in medicine. In addition to methodological problems that cause guidelines to be outdated rapidly, they are plagued by conflicts of interest. They are largely consensus opinions of panels of experts, most of whom are supported by industry. Professional societies, health insurers, Centers for Medicare and Medicaide Services, and dialysis providers also benefit from guidelines. Little attention is paid to the potential for harm to patients, and to the profession of medicine, from the widespread use of guidelines.