The aim of this study was to investigate the demographic, clinical characteristics, and service systems of patients with autism spectrum disorder (ASD) and/or intellectual disability presenting to a large paediatric hospital emergency department (ED) with behaviours of concern (BOC) over a two-year period. Retrospective audit of ED presentations with BOC in patients with ASD and/or intellectual disability from 1 January 2019 to 31 December 2020, at the Royal Children's Hospital, Melbourne, Australia. There were 124 presentations (84 patients) in 2019 and 129 presentations (82 patients) in 2020. The mean age was 11.7 years. 55% arrived by ambulance, 24% required physical restraint, and 26% required sedation. Re-presentation was predicted by single-parent household, child protection involvement, and requirement of an interpreter. Children and adolescents with ASD and/or intellectual disability regularly present to ED with BOC. New models of care are required to better support this highly vulnerable patient group. [ABSTRACT FROM AUTHOR]