This study estimates excess cost and length of stay associated with voluntary patient safety event reports at 3 hospitals. Voluntary patient safety event reporting has proliferated in hospitals in recent years, yet little is known about the cost of events captured by this type of system. Events captured in an electronic reporting system at 3 urban community hospitals in Portland, Oregon, are evaluated. Cost and length of stay are assessed by linking event reports to risk-adjusted administrative data. Hospital stays with an event report are 17% more costly and 22% longer than stays without events. Medication and treatment errors are the most expensive and most common events, representing 77% of all event types and 77% of added costs. Ninety percent of events result in no measurable harm. Patient safety events captured by voluntary event reporting reflect significant waste and inefficiency in hospital stays.