The cost of adverse events has recently become a point of scrutiny, as the Centers for Medicare and Medicaid Services recently announced it will no longer reimburse hospitals for costs associated with certain adverse events. This case-control study used data from the Critical Care Safety Study to determine the costs associated with adverse events in medical and cardiac intensive care unit patients. Adverse events were associated with increased costs of nearly $4000 per patient, which were only partially due to the increased length of stay (1 full day) associated with an adverse event.