For 20 years, the U.S. government has urged companies, universities, and other institutions that conduct clinical trials to record their results in a federal database, so doctors and patients can see whether new treatments are safe and effective. Few trial sponsors have consistently done so, even after a 2007 law made posting mandatory for many trials registered in the database. In 2017, the National Institutes of Health (NIH) and the Food and Drug Administration (FDA) tried again, enacting a long-awaited “final rule” to clarify the law’s expectations and penalties for failing to disclose trial results. The rule took full effect 2 years ago, on 18 January 2018, giving trial sponsors ample time to comply. But a Science investigation shows that many still ignore the requirement, while federal officials do little or nothing to enforce the law.