The randomized clinical trial (RCT) is often referred to as the gold standa
rd for the assessment of treatment efficacy. RCTs are receiving greater att
ention in the literature and higher priority by funding agencies than they
have in the past. In this paper, the basic principles of clinical trial des
ign are reviewed using examples from the neurosurgical Literature. The impo
rtance of designing the trial to answer one question well is emphasized.