Vaccine-preventable diseases continue to occur among adolescents (i.e., persons aged 11-21 years). In 1996, the Advisory Committee on Immunization Practices (ACIP), the American Academy of Pediatrics, the American Academy of Family Physicians, and the American Medical Association published joint recommendations emphasizing appropriate vaccination of adolescents aged 11-12 years who have not been vaccinated with hepatitis B vaccine, a second dose of measles, mumps, and rubella vaccine (MMR), varicella vaccine (if indicated), a booster dose of tetanus and diphtheria toxoids (Td), and other vaccines that may be indicated for certain adolescents. School entry requirements are an effective mechanism for ensuring high vaccination coverage among children. At the start of the 1997-98 school year, an amendment to the Florida Administrative Code (64D-3.011, F.A.C.) was instituted that requires all persons entering seventh grade to be vaccinated with three doses of hepatitis B vaccine, a second dose of MMR, and a Td booster, or to be on schedule for vaccination (i.e., having received at least one dose of hepatitis B vaccine, one dose of MMR, and a Td booster). To determine vaccination coverage among students entering seventh grade in Florida and in Orange County in 1997, CDC, in collaboration with the Florida Department of Health, analyzed state vaccination coverage data. This report summarizes the results of the analysis and indicates that a vaccination requirement for middle school entry can be effective in ensuring vaccination of adolescents.