Objectives: The health care system in Japan has undergone major changes, with increasing focus on specialization and continuity of care in its organization and delivery. Reducing the average length of stay is central to this plan. Readmission is often seen as an avoidable consequence of early discharges. And therefore, the readmission rate is used to assess the quality and efficiency of care. In this study, the main subjects in the implementation of readmission rate as an indicator are laid out and the framework for readmission in acute myocardial infarction (AMI) patients is applied. Methods: Literature review concerning readmission in AMI patients was conducted to understand the key points of the framework of the readmission. We then used insurance claims data to implement readmission as an indicator. The study sample consisted of 2,332 patients hospitalized due to AMI in Kyoto Prefecture from April 2009 to March 2010. Results: The 30-day readmission rate after AMI discharge was 3.7% (87/2,332), with the majority of these admissions due to coronary disease (38%). This rate was extremely low compared to the results reported in other countries, with readmission rates as high as 20% observed in the US. However, we observed that countries with high readmission rates had correspondingly short lengths of stay (LOS), and countries such as Germany and Japan with low readmission rates had long LOS. Conclusions: The readmission rate in Japan is low compared with those in other countries although mean LOS is long. The use of readmission rate may have applications in understanding trends in healthcare quality as Japan attempts to reduce LOS durations.