Randomized controlled trials (RCTs) are accepted as the "gold standard" for providing the best evidence for research. However, their application in clinical practice or health policy is limited by ethical considerations, the low feasibility and/or the lack of consistency. For resolving the limitations, clinical epidemiology that is comprised of the results of various studies, including cohort studies, case-control designs and outcome studies, or health administrative data can be applied as a new model for clinical research and decision making, and this leads in due course, to changes in health policy. Clinical epidemiology may serve as an alternative in which RCTs are not possible. Also, the merit of clinical epidemiology lies in that it is comprised of a wide range of data and that the collection of a large study population is possible from research studies conducted in dissimilar settings. However, methodological issues regarding the quality of data and the potential bias should be established. Clinical epidemiology will be a new approach to achieve the ultimate goal of medical research, which is to procure evidence through verification of causality. To develop a proper model for clinical epidemiology, it is imperative that more clinicians and health policy makers become involved in all aspects of clinical research, such as setting priorities, developing infrastructure and funding.