The randomized clinical trial is the preferred research design for evaluating competing diagnostic and therapeutic alternatives, but confidence in the conclusions from a randomized clinical trial depends on the authors' attention to acknowledged methodologic and statistical standards. This survey assessed the level of attention to the problem of multiple comparisons in the analyses of contemporary randomized clinical trials. Of the 67 trials surveyed, 66 (99 percent) performed multiple comparisons with a mean of 30 therapeutic comparisons per trial. When criteria for statistical impairment were applied, 50 trials (75 percent) had the statistical significance of at least one comparison impaired by the problem of multiple comparisons, and 15 (22 percent) had the statistical significance of all comparisons impaired by the problem of multiple comparisons. Although some statistical techniques are available, there still exists a great need for future work to clarify further the problem of multiple comparisons and determine how the impact of this problem can best be minimized in subsequent research.