Currently, no reliable method exists for comparing patient safety between hospitals. The hospital standardized mortality ratio, which compares observed with expected mortality for specific diagnoses, is widely used but has been decried as inaccurate and subject to gaming. Similarly, deaths in patients with low-mortality diagnoses are also used to identify safety problems, but these events are rare and unpredictable in many cases. Adverse events are known to result in longer hospitalizations. This Dutch study used a national database to examine whether unexpectedly long length of stay could be used as an indicator of the safety and quality of care. This preliminary study found that rates of unexpectedly long hospital stays varied widely between hospitals and were correlated with other quality measures. Although much more work is required to validate this measure, it may fill a need as a measure of patient safety that allows comparisons between hospitals.