BACKGROUND.: This phase 3b randomized, open-label study evaluated the immunogenicity and safety of coadministration of a hepatitis A and/or B vaccine with a quadrivalent oligosaccharide meningococcal CRM197-conjugate vaccine (MenACWY-CRM), in the context of an accelerated hepatitis A and/or B immunization schedule. METHODS.: A total of 252 healthy adult subjects were randomized to three groups to receive hepatitis A/B only (HepA/B), hepatitis A/B coadministered with MenACWY-CRM (HepA/B+MenACWY-CRM), or MenACWY-CRM only (MenACWY-CRM). Hepatitis A and/or B vaccination was administered in the form of a single booster dose or a primary three-dose series, depending on the hepatitis A and/or B vaccination history of subjects. Antibody responses to hepatitis A/B vaccination were assessed 1 month following the last hepatitis A and/or B dose. Serum bactericidal activity with human complement (hSBA) against meningococcal serogroups A, C, W-135, and Y was assessed 1 month post-MenACWY-CRM vaccination. Safety was monitored throughout the study. RESULTS.: At 1 month following the final hepatitis A and/or B vaccination, concomitant administration of hepatitis A/B and MenACWY-CRM was non-inferior to administration of hepatitis A/B alone in terms of geometric mean concentrations of antibodies against the hepatitis A and B antigens. One month post-MenACWY-CRM vaccination, the percentages of subjects achieving hSBA titers ≥8 for serogroups A, C, W-135, and Y in the HepA/B+MenACWY-CRM group (76, 87, 99, and 94%, respectively) were comparable to those in the MenACWY-CRM group (67, 82, 96, and 88%, respectively). The percentages of subjects reporting adverse events (AEs) were similar across study groups and a majority of the reported AEs were mild to moderate in nature. There were no study vaccine-related serious AEs. CONCLUSIONS.: MenACWY-CRM can be administered concomitantly with a hepatitis A and/or B vaccine in the context of an accelerated hepatitis A and/or B immunization schedule without increasing safety concerns or compromising the immune responses to any of the vaccine antigens. [NCT01453348]