This International Standard, based upon ISO/IEC 17025 and ISO 9001, provides requirements for competence and quality that are particular to medical laboratories. While this International Standard is intended for use throughout the currently recognized disciplines of medical laboratory services, those working in other services and disciplines will also find it useful and appropriate. In addition, bodies engaged in the recognition of the competence of medical laboratories will be able to use this International Standard as the basis for their activities. The Japan Accreditation Board for Conformity Assessment (AB) and the Japanese Committee for Clinical Laboratory Standards (CCLS) are jointly developing the program of accreditation of medical laboratories. ISO 15189 requirements consist of two parts, one is management requirements and the other is technical requirements. The former includes the requirements of all parts of ISO 9001, moreover it includes the requirement of conformity assessment body, for example, impartiality and independence from any other party. The latter includes the requirements of laboratory competence (e.g. personnel, facility, instrument, and examination methods), moreover it requires that laboratories shall participate proficiency testing(s) and laboratories' examination results shall have traceability of measurements and implement uncertainty of measurement. Implementation of ISO 15189 will result in a significant improvement in medical laboratories management system and their technical competence. The accreditation of medical laboratory will improve medical laboratory service and be useful for patients.