Large employers formed the National Committee for Quality Assurance (NCQA) to ensure value to healthcare purchasers. Value in healthcare is a function of quality divided by costs. Through NCQA's role as an accrediting agency for healthcare organizations and the development of performance measures, Health Plan Employer Data and Information Set (HEDIS), gains toward defining the value of health services have materialized. An analysis of the impact of HEDIS data collection on physician practices and the influence of HEDIS data on employer, employee, and governmental health plan selections is examined. This study consisted of a general review, from 1993 to 2001, of HealthStar databases, PubMed databases, and the NCQA website. NCQA accreditation is accepted as an important industry milestone for health plans, credentials verification organizations, and physician organizations. The data for HEDIS is collected from health plan administrative data repositories, whereas health plan members' clinical data may be collected by chart abstraction in physician offices. Data collection in physician offices consumes administrative resources from physician practices and health plans. As commercial and governmental insurers move toward greater adoption of HEDIS measures, complex implications are created for physician practices and vulnerable populations. There are lingering questions regarding the improvements in quality of care for medically underserved populations and physician practice costs attributable to HEDIS.