This brief note is an update to the “Medical Writing Tip of the Month” article on clinical trial registration in CHEST (March 2007).1 ClinicalTrials.gov (http://clinicaltrials.gov/), which currently contains > 73,000 registered trials, is operated by the National Institutes of Health. Although ClinicalTrials.gov continues to support a wide range of trial registration policies, including that of the International Committee of Medical Journal Editors (ICMJE),2 we want to call your attention to a new US law. On September 27, 2007, Congress enacted the Food and Drug Administration Amendments Act (FDAAA) [United States Public Law 110-85], which expands the legal requirements for registration beyond previous US law and mandates results reporting.3 Violations are subject to penalties. While the information presented previously on how to register at ClinicalTrials.gov continues to apply, we briefly describe changes to the registration requirements under FDAAA (see http://prsinfo.clinicaltrials.gov/fdaaa.html for more information). Reporting results at ClinicalTrials.gov is addressed in the companion “Medical Writing Tip of the Month” article in this issue of CHEST.4