A clinical trial cannot be adequately interpreted without information about the methods used in the design of the study and the analysis of the results. To determine the frequency of reporting what we consider 11 important aspects of design and analysis, we surveyed all 67 clinical trials published in the New England Journal of Medicine, the Lancet, and the British Medical Journal from July through December 1979 and in the Journal of the American Medical Association from July 1979 through June 1980. Of all 11 items in the 67 trials published in all four journals, 56 per cent were clearly reported, 10 per cent were ambiguously mentioned, and 34 per cent were not reported at all. At least 80 per cent of the 67 trials reported information about statistical analyses, statistical methods used, and random allocation of subjects, yet only 19 per cent reported the method of randomization. Loss to follow-up was discussed in 79 per cent of the articles, treatment complications in 64 per cent, and admission of subjects before allocation in 57 per cent, but eligibility criteria for admission to the trial appeared in only 37 per cent. Although information about whether patients were blind to treatment was given in 55 per cent, information about whether there was blind assessment of outcome was reported in only 30 per cent. The statistical power of the trial to detect treatment effects was discussed in only 12 per cent of the articles. The clinical trials published in The New England Journal of Medicine reported 71 per cent of the 11 items, those in the Journal of the American Medical Association 63 per cent, those in the British Medical Journal 52 per cent, and those in the Lancet 46 per cent. These rates are significantly different (P less than 0.001). We recommend that editors improve the reporting of clinical trials by giving authors a list of the important items to be reported.