Performance measurement has become increasingly popular in the health care delivery system of the United States. Until recently, the hospital was the most commonly scrutinized setting. With the expansion of managed care and the resulting compilation of large administrative databases, interest in performance measurement beyond the hospital setting has increased considerably. In particular, the performance of health maintenance organizations is now being assessed and reported publicly. The performance of individual physicians is also garnering considerable attention. This paper summarizes some of the many developments in performance measurement in managed care. The Health Plan Employer Data and Information Set (HEDIS) is described in the context of the national Report Card Pilot Project and with respect to local report card projects emerging around the United States. The lessons learned are identified, particularly with respect to external auditing of HEDIS data. Finally, the new initiatives of physician profiling and outcomes reporting are discussed.