The increasing number of cases of serogroup C meningococcal disease in Scotland in the late 1990s coincided with the availability of a new meningococcal conjugate serogroup C (MCC) vaccine that, from 1999 onwards, was offered to all individuals aged <20 years. Annual incidence rates between 1994 and 2003 were calculated in 3 age groups (<5 years old; 5-19 years old; and >or=20 years old), and Poisson regression models were used to verify disease trends over time. Dramatic reductions (P<.05) in the incidence of serogroup C meningococcal disease were seen in target age groups: from 15.8 incidents per 100,000 subjects in 1999 (95% confidence interval [CI], 11.3-20.3) to 0.7 incidents per 100,000 subjects in 2001 (95% CI, -0.3 to 1.6), for subjects <5 years old, and from 6.7 incidents per 100,000 subjects in 1999 (95% CI, 5.1-8.3) to 1.5 incidents per 100,000 subjects in 2001 (95% CI, 0.7-2.3), for subjects 5-19 years old. An increasing incidence of serogroup B meningococcal disease in individuals 5-19 years old was clearly established before the campaign began. A 30% decrease in the case-fatality rate for individuals <20 years old was not significant (P=.1598). The MCC vaccine program has been highly effective in Scotland, leading to substantial reductions in serogroup C meningococcal disease and meningococcal mortality, with no adverse effects on other groups.