Historically, military recruits have been at high risk of acquiring meningococcal disease. Beginning in the 1940s, the US military relied on mass treatment with sulfadiazine to control outbreaks in training camps. In the 1960s, a vaccine was developed in response to the emergence of sulfadiazine-resistant strains. Since 1971, all new recruits in the US military have been immunized against Neisseria meningitidis during their first days of service. Serogroups represented in vaccines given to service members have changed over time: the quadrivalent (A, C, Y, W135) vaccine has been given since 1982. In the US military, meningococcal disease rates decreased by approximately 94% from 1964 to 1998. After initiating routine immunization in 1971, crude rates decreased sharply and have remained low; in addition, there have been few cases of disease caused by serogroups represented in contemporaneously administered vaccines. In the US military, immunizations have been effective for the prevention of disease caused by vaccine-homologous serogroups of N. meningitidis.