The long-term effect on serious disorders such as liver cancer, caused by the hepatitis B virus, or cervical cancer, caused by the human papilloma virus (HPV), remains to be seen. Despite this clear medical success, vaccines have become the focus of considerable social and ethical controversy. More recently, the media and cultural wars over immunization have focused on the measles vaccine and/or the use of thimerosal and their alleged relationships to autistic behavior. Pediatric immunization programs undoubtedly stand as one of the most important U.S. public health initiatives of the 20th century. From a public policy perspective, states have clear legal authority to mandate vaccination, and such measures have succeeded in dramatically reducing the incidence of disease and complications from many important infectious agents. A successful childhood vaccination program must balance constitutionally protected parental liberties with social responsibility.