Menactra® vaccine (MenACWY-D) was licensed in the United States in 2005 for persons 11-55 years of age, in 2007 for children 2-10 years of age, and in 2011 for infants/toddlers 9-23 months of age. We conducted two studies at Kaiser Permanente Northern California (KPNC), an integrated health care organization, to assess the safety of MenACWY-D in 2-10-year-olds and 9-23-month-olds receiving the vaccine during routine clinical care. We conducted observational, retrospective studies of MenACWY-D in 2-10-year-olds (October 2007-October 2010) and in 9-23-month-olds (June 2011-June 2014). We monitored all subjects for non-elective hospitalizations, emergency department visits, and selected outpatient outcomes (specified neurological conditions, hypersensitivity reactions and new-onset autoimmune diseases) up to 6 months after vaccination, depending on the study. Using a self-control risk-interval design, we calculated incidence rate ratios (IRRs) comparing outcomes during the post-vaccination risk interval (0-30 days) with those during more remote post-vaccination comparison intervals (31-60 and 31-180 days [children] or 31-75 days [infants/toddlers]). There were 1421 children aged 2-10 years and 116 infants/toddlers aged 9-23 months who received MenACWY-D. Approximately 30% of the 2-10-year-olds and 67% of the 9-23-month-olds were considered at increased risk of meningococcal disease. Among 2-10-year-olds, there was 1 hospitalization on post-vaccination day 5 for fever, which was considered possibly related to vaccination. The only significantly elevated outcome among 2-10-year-olds was cellulitis/abscess (2 cases occurred during the risk interval versus 0 during comparison interval; IRR not evaluable [NE], 95% CI: 1.42, NE). After medical record review, the 2 cases were considered unrelated to vaccination. Among 9-23-month-olds, no outcomes were significantly elevated after vaccination and there were no hospitalizations. There were no deaths observed during the three-year accrual and subsequent six-month surveillance period for either study. Immunization of infants and young children with MenACWY-D vaccine was not associated with any new safety concerns; however, these small studies had limited power to detect rare or uncommon safety events. ClinicalTrials.gov Identifiers are NCT00728260 and NCT01689155.