The Medicare Patient Safety Monitoring System (MPSMS) is a national surveillance project aimed at identifying the rates of specific adverse events within the Medicare population. Created under the auspices of the Department of Health and Human Services' Patient Safety Task Force, this surveillance system identifies adverse events from randomly selected inpatient Medicare discharges and administrative data. This system is immense in scope and provides national rates of adverse events by employing explicit review criteria for all patient safety topics. The MPSMS explicit review is a patient-centered process focusing on patient harm rather than provider or system error, and has the following features: normalized inter-rater reliability; lower cost-per-chart reviewed than the traditional clinical expert-based implicit review; and the potential for comparative analysis across time and health care systems. A limitation to our approach is the reliance on administrative data to complete any post-discharge surveillance required. This paper explores the precepts behind the MPSMS review process. Three principles—intent, relevance, and transparency—describe the conceptual underpinnings for our approach.