Aim: To explore immunisation rates and catch-up delivery to children admitted to hospital before and after an immunisation service was commenced. Methods: This pre- and post-intervention study examined 300 admissions prior to (cohort 1) and 300 following (cohort 2) the introduction of an immunisation service. Immunisation rates, documentation, catch-up delivery and accuracy of the Australian Immunisation Register (AIR) were examined. Results: On admission, 75% (cohort 1) and 89% (cohort 2) were up-to-date with immunisations. Immunisation history was documented in the medical record in 78% and requirement for catch-up documented in 10%. AIR was incorrect in one-third of cases. By 3 months following discharge, 28% (cohort 1) and 64% (cohort 2) of patients were immunised. Conclusions: Children admitted to hospital have lower immunisation rates than the national average. Documentation was poor, opportunities for catch-up were missed and AIR is error-prone. Catch-up rates increased following the introduction of an immunisation service.