Substantial numbers of clinical trials continue to be reported only in summary reports that present insufficient methodological details to permit informed judgments about the likely validity of the conclusions. Using a cohort of 176 controlled trials reported in summary form, we tested the hypotheses that they would be more likely to be followed by full reports if, on the basis of the information provided in the summary report, (1) the trial was judged to be methodologically sound, (2) the results favored the test treatment, and (3) the sample size was relatively large. The results of univariate and multivariate analyses provided support for only the third of these hypotheses. Investigators, as well as those who fund and sanction the conduct of clinical research, should make greater efforts to ensure that clinical trials are reported properly.