Delivery of good care, ability to communicate effectively about patient care and the decision-making during the care process depends on the quality of the information available to all professions and between sectors. The main purpose of an electronic health record is to support the multidisciplinary communication, cooperation and decision-making in the patient's care process. In addition, the data in electronic health records are used, e.g. in clinical research, health system management, the planning of health services and government reporting. A nationwide electronic health record will be introduced in Finland by the end 2007. Reaching this target has been a special part of the national health project. In a subproject of the introduction of a national electronic health record, core data elements of electronic health record have been defined through a consensus-based approach. The main elements are the patient identification information, the provider's identification information, care episode, risk factors, health patterns, vital signs, health problems and diagnosis, nursing minimum data set, surgical procedures, tests and examinations, information about medication, preventive measures, medical statements, functional status, technical aids, living will, tissue donor will, discharge summary, follow-up care plan and consent information. Furthermore, existing vocabularies, nomenclatures, classifications and codes were clarified. The HL7 Finland has defined the manner in which this information is expressed in the CDA R2 structure. The core information elements will be implemented in regional development projects which are partly funded by the Ministry of Social Affairs and Health. This paper presents the defining process of the national core data elements of electronic health record systems in Finland.