The lack of standardized, reliable and systematic coding of diagnoses in the outpatient sector renders the availability of valid epidemiological data impossible. Moreover, diagnoses are one of the essential key features for an assessment of the cost-effectiveness and a quality monitoring. One component for the prognosis of diagnoses is provided by the outpatient sector due to the use of the ATC code for prescriptions of pharmaceutical products. The other component, the ICD code, is used in hospitals to code diagnoses. Therefore, the department for Evidence Based Health Care in the Main Association of the Austrian Social Security Institutions has initiated a project which tries to derivate the ICD from the ATC code in order to obtain valid diagnoses for the outpatient sector.