Numerous initiatives promoting patient safety have been introduced throughout the United States but, so far, relatively few physicians seem to believe that these interventions will make medical practice safer. Possibly, physicians are unaware or existing evidence favors interventions, or they may feel that they cannot realistically be incorporated into medical practice. This survey was done to learn whether published evidence that interventions are effective does in fact reduce medical errors and influence physicians' estimates of their efficacy. A literature review sought evidence of efficacy for 13 interventions aimed at reducing medical errors. A questionnaire was sent to 1332 randomly chosen U.S. physicians. The 831 respondents were 62% of those surveyed. Interventions considered effective had been found, either experimentally or in controlled observational studies, to reduce medical errors, limit adverse events caused by such errors, or decrease mortality. Published evidence of efficacy was found for 6 of the 13 interventions. Physician estimates that a given intervention would be "very effective" ranged from 20% to 51% for interventions considered effective and from 6% to 55% for those lacking evidence of efficacy. On average, the respondents rated 34% of effective interventions and 29% of the others as being very effective. Physicians with an academic affiliation were likelier than the others to rate interventions as very effective whether or not there was published evidence of efficacy, but the difference was not statistically significant. When only interventions considered effective were considered, academic physicians and those in practice for longer periods rated more of them as being very effective. Measures to widen the use of effective safely interventions include research to gather more evidence of effectiveness and the adoption of means other than peer-review publications for disseminating the evidence. It could be helpful to incorporate evidence of efficacy into graduate medical education through curriculum changes or certification examinations. It will be very important to better understand organizational barriers to successfully implement effective patient safety interventions.