The number of good quality studies on the effect of feedback and reminders on diagnostic and preventive activities in ambulant practice is still low. The interventions and procedures studied differ widely, and the reporting of the results is insufficiently precise. This makes comparison difficult and quantitative pooling impossible. Nevertheless, the literature supports the contention that feedback reduces the use of diagnostic tests and the costs thereby engendered. It also discloses a positive effect of feedback on the adherence of medical practice to guidelines or standards. In this respect, the effect of reminders seems to exceed that of classical methods of feedback. There is still a need for research on the effect of feedback, reminders and other instruments for quality assurance on various aspects of medical performance in different settings.