Service quality in medical laboratories is influenced by a number of variables. Medical laboratories have long recognized the need for total quality management that incorporates the continuous improvement of all stages, such as the pre-analytical, analytical and post-analytical phases, of the diagnostic process, in addition to the traditional internal and external quality control of analytical procedures. Based on national and international experience, continuous improvement of quality and its external assessment are of high priority in order to guarantee a reliable, effective and cost-effective diagnostic service. Certification of health care services, according to ISO 9001 standards in Hungarian hospitals, is not sufficient to prove professional competence of medical laboratories, which called for a system of laboratory accreditation. Accreditation is an external professional audit by which an independent accreditation body gives formal recognition that the medical laboratory is competent to provide high quality services that are compliant with rigorous professional standards of best practice. The primary aim of accreditation is the improvement of the quality of diagnostic services by voluntary participation, professional peer review, continuous training and education and compliance with professional standards. In vitro medical laboratories have pioneered quality control and quality assurance in health care. Based on these strengths and traditions, the introduction of the accreditation program of medical laboratories in Hungary is one of the key professional and ethical responsibilities of diagnostic professions, in order to improve the quality, efficiency and effectiveness of laboratory services during the course of Hungary's accession to the European Union.