That it is not possible to find information about all initiated clinical trials is of international concern. This is a particular worry because scientists tend to publish their positive findings more often than their negative findings (publication bias). A comprehensive register of initiated clinical trials, with each trial assigned a unique identifier, would inform reviewers, physicians, and others (eg, consumers) about which trials had been started and directly address the problem of publication bias. Patients and their clinicians could also know which trials are open for enrollment, thus speeding medical advances. Individuals who participate in clinical trials typically provide consent in the belief that they are contributing to medical knowledge. But if the knowledge gained is never reported, the trust between patients and investigators and that between patients and research ethics review boards are both damaged. Ethical issues are of particular concern if industry is gaining financially from public involvement in trials, but refusing to reciprocate by making information from industry-sponsored trials generally available. All stakeholders-investigators, research organizations and institutions, journal editors, lawmakers, consumers, and others-must act now, together and in their own domains, to ensure comprehensive registration of clinical trials.