Administrative medical databases are massive repositories of data collected in healthcare for various purposes. Such databases are maintained in hospitals, health maintenance organisations and health insurance organisations. Administrative databases may contain medical claims for reimbursement, records of health services, medical procedures, prescriptions, and diagnoses information. It is clear that such systems may provide a valuable variety of clinical and demographic information as well as an on-going process of data collection. In general, information gathering in these databases does not initially presume and is not planned for research purposes. Nonetheless, administrative databases may be used as a robust research tool. In this article, we address the subject of public health research that employs administrative data. We discuss the biases and the limitations of such research, as well as other important epidemiological and biostatistical key points specific to administrative database studies.