Imprisonment has been linked to poor mental and physical health outcomes with the period following release identified as being particularly challenging. This population-based study examined emergency department (ED) utilisation in the 12 months following a release from imprisonment in New Zealand in 2018. Using national linked health and justice administrative datasets, demographic, incarceration, and diagnostic patterns in ED use post-release were examined. Of 13,686 individuals, 35% presented to the ED at least once, making up 10,734 ED presentations. Those aged 17-24 were the age group most likely to have an ED presentation (38%) and women were more likely than men to present to EDs over 12 months (41% vs 34%). Of the ED presentations, 3,897 (36%) resulted in 3+ hours of treatment in the ED or an inpatient ward, counted as a long-term ED (LT-ED) event. Those released from remand were 1.23 times (95% CI 1.15–1.31) more likely to have a LT-ED event compared to those released from prison. Thirty-eight percent of the LT-ED events were due to injuries; of which assault was the most common external cause. There were high rates of both ED presentations and LT-ED events in the first week after release. When comparing to literature, this cohort presented to the ED approximately 4 times more than the general NZ population. These findings demonstrate the significant health needs of individuals post-imprisonment and emphasise the need to prioritise those released from remand facilities within public health policy, research and practice.