A physician's ability to make conclusions about the relative efficacy of interventions based on their clinical experience is limited frequently. Therefore, surgeons commonly use research evidence to guide their clinical practice. The randomized controlled trial is the strongest study design. However, randomization in itself does not guarantee the trial results are valid (free from bias). Understanding the potential impact of various methodologic features of a randomized controlled trial allows a clinician to determine the validity of a trial. We present a guide for evaluating the validity of randomized controlled trials giving special consideration to issues confronted in surgical trials.