There are three potential sources of information for evaluating a clinician's performance: documentation, patient report, and directly observed care. Current measures draw on just two of these: data recorded in the medical record and surveys of patients. Neither captures an array of performance characteristics, including clinician attention to symptoms and signs while taking a history or conducting a physical exam, accurate recording in the medical record of information obtained during the encounter, evidence based communication strategies for preventive care counseling, and effective communication behavior. Unannounced Standardized Patients (USPs) have been widely deployed as a research strategy for systematically uncovering significant performance deficits in each of these areas, but have not been adopted for quality improvement. Likely obstacles include concerns about the ethics of sending health professionals sham patients, the technical challenges of the subterfuge, and concerns about the relatively small sample sizes and substantial costs involved. However, the high frequency of significant and remediable performance deficits unmasked by USPs, and the potential to adapt registration and record keeping systems to accommodate their visits, suggest that their selective and purposeful deployment could be a cost effective and powerful strategy for addressing a gap in performance measurement.