The study investigating reliability and validity of the ICD-10 codes will be done in detail: A prospective random selection of 700 patients, 200 patients from Health Trust Førde and 500 patients from the HUH, all having undergone major surgery. Present knowledge should suggest one or several major complications caused by procedures or iatrogenic causes in at least 17 % the surgical patients (de Vries, 2010). Then an inclusion of 700 patients is needed in order to find such complications in 119 cases. We will identify all post discharge ICD-10 codes for each patient. These codes will be thoroughly reviewed for accuracy and completeness by comparing to the actual information as documented by physicians and nurses in the EPJs throughout the total hospital stay. Primary outcome is here to investigate that registered ICD-10 codes have adequate sensitivity and specificity compared to the information in the patients' medical journal.