In an effort to control ambulatory care costs, regulatory practice guidelines (références médicales opposables or RMOs) were introduced by law in France in 1993. RMOs are short sentences, negatively formulated (“it is inappropriate to \ldots”), covering medical and surgical topics, diagnosis, and treatment. Since their introduction, physicians who do not comply with RMOs can be fined. The fine is determined by a weighted combination of indices of harm, cost, and the number of violations.The impact of the RMO policy on physician practice has been questioned, but so far few evaluations had been performed. At the end of 1997, only 121 physicians had been fined (0.1% of French private physicians). The difficulty of controlling physicians, the large number of RMOs, and the lack of a relevant information system limit the credibility of this policy.The simultaneous development of a clinical guideline program to improve the quality of care and of a program to control medical practice can lead to a misunderstanding among clinicians and health policy makers. Financial incentives or disincentives could be used to change physician behavior, in addition to other measures such as education and organizational changes, if they are simple, well explained, and do not raise any ethical conflict. But these measures are dependent on the structure and financing of the healthcare system and on the socioeconomic and cultural context. More research is needed to assess the impact of interventions using financial incentives and disincentives on physician behavior.