Objective: The purpose of this study was to clarify the importance of therapeutic drug monitoring (TDM) at acute care hospitals using Diagnosis Procedure Combination (DPC) data.<br>Methods: We used DPC data from about 3,500,000 inpatients at about 950 acute care hospitals.  The investigation period was from July 2010 to December 2010.  Patients were divided into 2 groups: TDM intervention (n=22,012); and non-TDM intervention (n=26,400).  We compared the clinical indicators (length of hospital stay, payment based on performance and drug costs) and use of antimicrobials.<br>Results: TDM intervention was carried out in 45.5% patients for whom an anti-MRSA agent was prescribed.  The duration of anti-MRSA agent administration was significantly longer in the TDM intervention group than in the non-TDM intervention group.  The total daily cost of anti-MRSA agents was significantly lower in the TDM intervention group than in the non-TDM intervention group.<br>Conclusion: Our results suggest that TDM intervention is often performed for seriously ill patients who require continuous treatment.  TDM intervention may prevent adverse reactions as a result of adjusting the dosage of the anti-MRSA agent.