BACKGROUND: We aimed to evaluate the Meningococcal (Neisseria meningitidis) C conjugated (MCC) vaccine seroconversion and adverse events (AEs) in HIV-infected and HIV-uninfected children and adolescents in Rio de Janeiro, Brazil. METHODS: HIV-infected or HIV-uninfected subjects, 2-18 years old, with CD4+ T-lymphocyte cell (CD4) percentage >15%, without active infection or antibiotic use, were enrolled. All patients were evaluated before and 1-2 months after immunization for seroconversion (defined as ≥4-fold titer increase in human serum bactericidal activity) and at 20 minutes, 3 and 7 days after immunization for AEs. Factors associated with seroconversion among HIV-infected group were studied. RESULTS: Two hundred four subjects were enrolled: 154 HIV-infected and 50 HIV-uninfected. Median age was 12 years, and 53% were female. Among the HIV-infected group, 82 (53%) had a history of at least 1 C clinical category of Centers for Diseases Control and Prevention event, and 134 (87%) were using combination antiretroviral therapy. The median nadir CD4 percentage was 13% (0-47%). Seventy-six (37.3%) experienced mild AEs. Seroconversion occurred in 46 of 154 (30%) in the HIV-infected group and in 38 of 50 (76%) in the uninfected group (P < 0.01). Factors associated with seroconversion in the HIV-infected group were as follows: never had a C clinical category event [odds ratio (OR) = 2.1, 95% confidence interval (CI): 1.0-4.4]; undetectable viral load at immunization (OR: 2.4, 95% CI: 1.1-5.2) and higher CD4 nadir/100 cells (OR: 1.1, 95% CI: 1.0-1.2). CONCLUSION: MCC vaccine should be administered to HIV-infected children and adolescents after maximum immunologic and virologic benefits have been achieved with combination antiretroviral therapy. Our data suggest that a single dose of MCC vaccine is insufficient for HIV-infected individuals 2-18 years of age.