 The Swedish National Patient Registry NPR is hosted by the Swedish Agency of Health and Welfare and contains all patient contacts within Sweden with a coverage of 90 for orthopaedic diagnoses. Registered are main diagnosis and co-morbidity using the ICD-9 code until 1996 and from 1997 onward ICD-10 codes. Treatment is coded since 1996 using the Swedish classification of surgical procedures. Furthermore, information on hospitalisation time is available from the registry. 