This descriptive study analyzed nearly 100,000 reports from 26 acute care hospitals with investigators discovering wide variations in reporting rates across sites. The most common classification included medication-related events, and more than half of all events affected a patient before being caught. The authors report that nurses were the most frequent users of the electronic reporting systems, whereas physicians accounted for an overwhelming minority. A past study found similar underuse of reporting systems by physicians and recommended alternative methods for capturing physician-based information about adverse events.