In 2000, the National Institutes of Health (NIH) established ClinicalTrials.gov in response to congressional action 2 years earlier.1 Sponsors were required to register only those clinical trials assessing drugs for treatment of serious or life-threatening diseases. Compliance with even this limited scope of required registration was poor until 2 related events occurred in 2004: first, in June of that year, the New York State attorney general sued GlaxoSmithKline for failing to publish the negative results of a trial of paroxetine in pediatric patients.2 Second, in September, the International Committee of Medical Journal Editors announced that, effective July 2005, reports of clinical trials would be accepted for publication only if the trials had been properly registered.3 The number of trials registered on ClinicalTrials.gov increased substantially after these events.4