A randomized controlled trial (RCT) is the most definitive tool for evaluation of the effectiveness of an intervention and can establish a cause-and-effect relationship between an intervention and an improved disease outcome. However, the undertaking of an RCT does not guarantee valid results, and the findings of RCTs of the same intervention are often discrepant. While many reported trials are of high quality, a significant number have deficiencies in design, conduct, analysis, or interpretation of results. Medical practitioners must become familiar with the methodology of RCTs in order to assess the validity of the reported findings and the relevance of the results to their own patients. Trialists must report sufficient information about the methods used so that readers can judge for themselves if the trial worked as planned.