Today the discharging physician reviews the medical journal and makes a medical summary including coding diseases and complications relevant for the current admission. International Classification of Diseases (ICD-10) codes are used to set diagnoses for clinical, epidemiological and quality purposes (http://www.who.int/classifications/icd/ICD10Volume2_en_2010.pdf). The ICD-10 codes are also used for registrations on national mortality and morbidity in the Norwegian National Patient Register (NPR). Questions have been raised as to the accuracy and quality of the data in such registers in Norway, e.g. in patients with sepsis (Flaatten, 2004), and intensive care patients (Aardal et al., 2005). In a Danish study on relations between ICD-10 coding in the National Registry of Patients and the hospitals' discharge summary and medical records, a high reliability between ICD-10 scores and co-morbidity was found (Thygesen et al., 2011). To our knowledge similar studies have not been done in Norway. As a crucial part of this investigation we concurrently will evaluate the reliability and validity of our patient administrative data by comparing the post discharge ICD-10 codes to actual data available directly from medical journal systems as documented by health care personnel in the journal texts.