Several studies have indicated that differences in medical practice are often an important factor behind variations in resource utilization. 'Practice', in medical contexts, is used as a comprehensive expression for what is regarded to be adequate care, considering science and proven experience, as well as present resources, demography, organization, and other given conditions. However, experience shows that routines and practice, even under similar conditions (resources, organization, etc.) often vary significantly among departments within the same medical discipline. In this more restricted sense, variations in practice might depend on different--more or less well-founded--opinions among physicians concerning what constitutes appropriate length of stay, level of care, and technology. With examples from some specialties (e.g. general surgery, obstetrics and gynecology), we demonstrate this 'model' and the economic impact of practice variations. Our conclusion is that there are opportunities for achieving greater benefit from existing resources, i.e. increasing efficiency, through reallocation and alternative utilization of resources, altered practice.