The Office of the Inspector General (OIG) has conducted a series of analyses of adverse event incidence among Medicare beneficiaries. This report evaluates how hospitals, the Centers for Medicare and Medicaid Services (CMS), and state agencies have responded to particularly serious adverse events. The OIG found that investigations into errors were generally timely and resulted in changes with the potential to improve patient safety. However, the OIG faults state agencies for failing to communicate findings to The Joint Commission and for failing to monitor long-term safety performance at hospitals where errors occurred. The report outlines specific recommendations for CMS and state agencies to ensure that lasting safety improvement comes about after serious errors occur.