OBJECTIVES: Emerged evidence has linked non-steroidal anti-inflammatory drugs (NSAIDs) to cardiovascular adverse outcomes. Specifically, parenteral NSAIDs such as ketorolac were associated with higher risk of adverse outcomes than oral ones. Recent policy concern has therefore focused on the rational use of parenteral NSAIDs. Using 2000-2009 Taiwan's National Health Insurance research database (NHIRD), the objective of this study was to provide an estimate of off-label use of ketorolac in a nationally representative sample. METHODS: Inpatient (n=303,733) and outpatient prescriptions (n=605,750) of parenteral ketorolac from 2000 through 2009 were identified from a random sample of 1,000,000 individuals in NHIRD in 2005.  Ketorolac prescribing outside the indications approved by the Taiwan Food and Drug Administration (i.e. short term use (≤ 5 days) for postoperative pain) was defined as off-label use. Differences in patient and prescriber characteristics between licensed and off-label prescriptions were assessed with chi-square tests for categorical variables and t-tests for continuous variables. RESULTS: Off-label use of ketorolac was estimated to be 28.5% at the inpatient settings. The off-label use was more frequent at the outpatient settings (90% of the outpatient prescriptions), with the highest proportion of off-label use among pediatric patients (<6 years old (y/o): 97.2%, 6-18 y/o: 95.8%, 18-65 y/o: 95.1%, and >65 y/o: 94.7%).  Approximately 50% of the outpatient off-label prescriptions of ketorolac came from metropolitan hospitals. Also, the majority of the outpatient off-label prescriptions of ketorolac were prescribed by the emergency departments. CONCLUSIONS: Our results suggest that the actual extent of off-label use of ketorolac could be very high, especially at the outpatient settings. It highlights the need for a better understanding of the reasons behind this phenomenon, a more appropriate definition of the role of ketorolac in pain managements, and a more efficient policy intervention to rationalize the use of ketorolac.