The Japanese government has introduced the casemix system for the acute-care hospitals since 2003. The applied casemix system is DPC (Diagnostic Procedures Combination) that was newly developed in Japan. The basic idea of DPC is to classify a patient by the combination of diagnosis and procedures conducted within the hospitalization. The first key of classification is diagnosis, and then types of procedures are considered to decide a particular group. One of the main purposes of DPC project is to implement a standardized dataset of in-patient acute care. The keywords are transparency and accountability. Using this framework, we can evaluate the process of medical services. The DPC project collects the three types of information: Form 1 is a clinical summary that contains information on diagnosis and severity. E file has information of the bundled charge of procedure and F-file indicates the detail of bundled procedures. Form 1, E-file and F-file are matched according to the ID number that is unique for each discharged case. Using these data, we can describe the process of each in-patient treatment. As the DPC scheme covers more than 8 million of acute in-patients cases in Japan, it has become one of the important sources of information for clinical analyses, such as patterns of pharmaceutical use and interventional treatments. Furthermore, DPC database can be used for a large-scale multi-center post-marketing clinical study. It is expected that more epidemiologists would have much interest for use of DPC data for studies of clinical epidemiology and health service researches.