[ICD and OPS. Historical development and current situation]

This survey describes some general problems of medical classifications and their historical development at international and national levels. The emphasis is on the "International Statistical Classification of Diseases and Related Health Problems (ICD)" of the World Health Organization (WHO). Evolving from an "International List of Causes of Death", initiated more than 100 years ago, particularly since 1948 the ICD has increasingly developed into an internationally essential classification also for all problems of morbidity. In Germany, the implementation for the mandatory coding of diagnoses of inpatients began with ICD-8 in 1968. With the 10th revision (ICD-10) the coding of diagnoses of all inpatient and outpatient cases became mandatory in the year 2000. Since 2004 this specific German version is called ICD-10-GM and revised yearly. No internationally valid classification is available for operations and other medical procedures. "The International Classification of Procedures in Medicine (ICPM)", published by the WHO in 1978, has not been revised since, but served as a model for several national classifications. Also the German "Operationen- und Prozedurenschlüssel (OPS)" (Code of Operations and Procedures), initially published in 1994, derives from the ICPM. Since 2004 both the ICD-10-GM und the OPS are revised yearly. This paper shows historical development, contents and areas of application for ICD-10-GM and OPS. In the case of inpatient treatment, the classifications are mainly used for reimbursement based on the German G-DRG System, in the case of outpatient treatment for the legally required coding of diagnoses and other reasons for medical treatment and of selected surgical procedures for reimbursement purposes.