Clinical trials can be terminated early for one of three reasons: there is a preponderance of adverse events in one arm, or both arms have more than the expected number of them; an interim analysis shows that no significant effect will be found with the projected number of participants (futility); or an interim analysis shows the clear superiority in the experimental condition. There is little controversy regarding truncating studies because of adverse events, but ending trials early because of futility, and especially for apparent superiority, is more controversial. Estimates of treatment effect early in the trial are based on smaller sample sizes, and hence the confidence intervals around those estimates are broad. There is much evidence that early estimates of treatment effect are inflated compared to trials of the same intervention that are completed. This likely does not constitute fraud or misconduct, but does reflect poor practice unless stringent criteria are followed.