Background: The rapid response system (RRS) aims to prevent unexpected cardiac arrest by responding to the deteriorating condition of hospitalized patients at an early stage. In this study, we evaluated the status of the RRS 5 years after its introduction in St. Marianna University School of Medicine Hospital. Methods: We retrospectively analyzed the medical emergency team (MET) request data of our hospital for the period of June 2010-May 2015. We compared the status of the RRS before and after the introduction of the critical care outreach team (CCOT) in August 2014. Results: There were 197 MET requests over the five-year period, with an increasing trend in the number of requests. Acute altered mental status was the most common reason for MET activation, followed by oxygen desaturation (measured by a pulse oximeter) < 90%, hypotension (blood pressure <90 mmHg), and cardiopulmonary arrest (CPA). The general ward requested the MET most frequently (62.9%). Overall, 47.7% of METactivated patients were transferred to intensive care unit, and 21.3 % were "non-transfer" cases. MET activation by general wards (55.6% vs. 78.1%, P=0.0017) and MET activation by CPA significantly increased (9.0% vs. 29.7%, P=0.0003) after the introduction of the CCOT, while the one-month survival/survival-to-hospital discharge rate significantly decreased (75.2% vs. 57.8%, P=0.0143). Discussion and Conclusion: Over the 5 years, the number of MET requests increased, especially after the introduction of the CCOT. When RRS was required due to cardiopulmonary arrest, the patient's condition had already deteriorated, and this was considered to have reduced the survival rate of RRS-activated patients. Comparing the data before and after the introduction of CCOT showed results different from the expected effect of RRS, probably because the RRS is usually triggered after a patient's condition clearly deteriorates. In the case of a cardiopulmonary arrest, when the patient's condition had already deteriorated and the number of CPA-related requests increased, a decrease in the survival rate was considered. Therefore, efforts must be made to request MET at an earlier stage and to use the Code Blue System to enable an earlier response for cases of cardiopulmonary arrest. Keywords Rapid response system, medical emergency team, critical care outreach team, cardiopulmonary arrest, 1-month survival/survival to discharge rate wards in the hospital, including the general ward; the attached emergency and critical care center included 10 beds in the ICU, six beds in the coronary care unit (CCU), four beds in the stroke care unit (SCU), and 32 beds in the high care unit (HCU).