Variations in medical practice are well documented, but there has been less progress in explaining these variations. This paper discusses the existing theories and hypotheses and concludes that a change in theoretical approach is required, to one that more directly highlights the social context influencing the behaviour of doctors in their daily practice. An initial alternative model for explaining variation in practice style is presented. The paper illustrates how (combinations of) important structural factors, such as the availability of hospital resources, the way the doctor is reimbursed, the availability of patients, professional uncertainty, and the way the hospital is financed, lead to hypotheses about when different local standards of medical care emerge. It is concluded that theoretical progress in research on variations in medical practice is possible and that empirical research needs to be driven by hypotheses that emphasize the role of social contexts in the doctor's decision behaviour. Some suggestions for future lines of research are outlined.