An accurate understanding of the frequency, severity, and preventability of adverse events is required to effectively improve patient safety. This study included review of more than 2,800 inpatient records from 11 American hospitals with nearly one quarter having at least one preventable or not preventable adverse event. Overall, approximately 7% of all admissions included at least one preventable event and 1% had a severity level of serious or higher. An accompanying editorial by Dr. Donald Berwick sees the results of this study as a needed stimulus for leadership to prioritize patient safety anew.