1. Groups of licensed physicians and osteopaths engaged in the practice of medicine or surgery in a particular area, formed to ensure adequate review of the services provided by the various medical specialties and subspecialties in the area, as well as providing DRG validation. 2. A group of physicians working with the government to review cases for hospital admission and discharge under government guidelines. Under the Medicare program, PROs are known as Quality Improvement Organization (QIO) programs. See also peer review and Quality Improvement Organization (QIO) program.