Fewer than half of children receive all recommended immunizations on time. Hospitalizations may be opportunities to address delayed immunizations. Our objectives were to assess (1) prevalence of delayed immunizations among hospitalized patients, (2) missed opportunities to administer delayed immunizations, and (3) time to catch up after discharge. METHODS:We conducted a retrospective cohort study investigating immunization status of patients 0 to 21 years of age admitted to an academic children's center from 2012 to 2013 at the time of admission, at discharge, and 18 months postdischarge. Immunization catch-up at 18 months postdischarge was defined as having received immunizations due on discharge per Centers for Disease Control and Prevention recommendations. x 2 and t test analyses compared characteristics among patients caught up and not caught up at 18 months postdischarge. Analysis of variance and logistic regression analyses compared mean number of immunizations needed and odds of immunization catch-up among age groups. Kaplan-Meier and Cox proportional hazards analyses compared catch-up time by age, race, sex, and insurance.RESULTS: Among 166 hospitalized patients, 80 were not up to date on immunizations at admission, and only 1 received catch-up immunizations before discharge. Ninety-nine percent (79 of 80) were not up to date on discharge per Centers for Disease Control and Prevention recommendations. Thirty percent (24 of 79), mostly adolescents, were not caught up at 18 months postdischarge. Median postdischarge catch-up time was 3.5 months (range: 0.03-18.0 months). Patients 0 to 35 months of age were more likely to catch up compared with those of other ages (hazard ratio 5 2.73; P 5 .001), with no differences seen when comparing race, sex, or insurance.CONCLUSIONS: Pediatric hospitalizations provide important opportunities to screen and immunize children.