The United States has made tremendous progress in using vaccines to prevent serious, often infectious, diseases. But concerns about such issues as vaccines' safety and the increasing complexity of immunization schedules have fostered doubts about the necessity of vaccinations. We investigated parents' confidence in childhood vaccines by reviewing recent survey data. We found that most parents--even those whose children receive all of the recommended vaccines--have questions, concerns, or misperceptions about them. We suggest ways to give parents the information they need and to keep the US national vaccination program a success.